Physics and Chemistry 3 Teacher's Guide sample unit

DEMO

3

SECONDARY EDUCATION

Physics and Chemistry J . M. Víl c h e z G o nz ál e z , A. M .ª M o ral es C as , G. V i l l al o b o s G al de ano

T e a c h e r’s G u i d e

Building

Blocks

3

Secondary education

Physics and Chemistry Teacher’s Guide

Building Blocks is an educational project of Anaya Educación for Secondary Education with the participation of: K. Chambers, Danny Latimer, R. Oakes, J. Roe, Hannah Peat, Karen Piper, Denise Suárez, Begoña Fuente Larrazabal, Sara Gascón Martín, Armando Caracheo, José Miguel Vílchez González, Ana María Morales Cas and José Gabriel Villalobos Galdeano.

The following people have worked on this book:

Editorial team: Manuel Gil, Margarita Marcos, María Ferrond, Sergio Gutiérrez and Denise Suárez Design, technical drawings and maps: Patricia G. Serrano, Juan Carlos Quignon, Julio Vázquez and Miguel Ángel Díaz-Rullo

Illustrations: M.a Carmen Fuente and Pablo Vázquez Layout: DiScript and Coral Muñoz CORRECTIONS: Anaya Corrections departament Graphic edition: Beatriz Gutiérrez Translation: Montero Language Services Proofreading and unit opening pages: Armando Caracheo Photographs: AEMET, AGE fotostock (Arco/R. Priemer, Charles D Winters, DAVID PARKER, Fine Art Images, Jim West, Jo Deleker, JUNIORS BILDARCHIV, Mary Evans Picture Library, PROF PETER FOWLER/ SC, SCIENCE PHOTO LIBRARY, Science Source, Sohns/imageBROKER, The Granger Collection, US DEPARTMENT OF ENERGY), Agencia EFE (MG), Alamy/Cordon Press (Historic Images, Panther Media GmbH, Roger Sedres, Science History Images, Zoonar GmbH), Archivo Anaya (Alcón, A.; Santos, V. E.; Cosano, P.; Hernández Moya, B.; Martín, J. A.; Martínez, C.; Osuna, J.; Padura, S.; Peñuela Py, E.; Steel, M.; Sánchez, J.), Dreamstime, Dres Esther Vázquez y Ugutz Unzueta del grupo de Nanobiotecnología de la Universidad Autónoma de Barcelona (UAB), Getty images (Altayb, Bloomberg), Istock/Getty images, NASA (NASA’s Goddard Space Flight Center, NASA, ESA, y Z. Levy (STScI)), 123 RF y colaboradores.

Academic and Professional Orientation: created in conjunction with Fundación Bertelsmann. Coordinator: Juan José Juárez Calvo. Expert collaborators: Sara Lozano Santiago, Belén Pérez Castro and Pilar Vázquez Hernández.

Commitment to Sustainable Development Goals Our publications contain carefully selected content, illustrations and language to comply with non-discrimination on the grounds of gender, culture or opinion.

Grupo Anaya considers social and environmental responsibility to be one of its fundamental values.

For this reason, we are committed to: · continually improving our contents and materials related to the environment. · reducing our carbon emissions. · using natural resources responsibly. · making sure that our activity has no negative consequences for endangered forests.

These commitments, among others, mean that 100% of the paper used in our books has the PEFC label.

Important information: The activities proposed in this book should be completed in a separate notebook or on sheets of paper, not in the book itself.

The links to webpages which appear in this book have been checked before printing. The publisher cannot be liable for any changes or modifications which occur after the date of publication.

© GRUPO ANAYA, S.A., 2021 - C/ Juan Ignacio Luca de Tena, 15 - 28027 Madrid.

All rights reserved. No part of this publication may be reproduced, stored in a retrieval system, or transmitted, in any form or by any means, electronic, mechanical, photocopying, recording, or otherwise, without the prior permission of the publishers.

Index Building blocks and project keys ........................................

4

Our project ........................................................................................

6

Units Scientific knowledge ...................................................................

8

1. Matter. Gases .............................................................................

20

2. The atom ......................................................................................

34

3. Chemical substances ............................................................

46

4. Chemical reactions ...............................................................

60

5. Force and its effects .............................................................

76

6. Nature of forces .......................................................................

98

7. Circuits ...........................................................................................

116

8. Energy sources .........................................................................

138

BUILDING

BLOCKS

A project that is rooted in skills-based learning and the development of student commitment within the realities of available time.

Building Blocks is a new skills-based approach, with the utmost curricular rigour and a coherent and coordinated content sequence in the areas throughout the entire educational stage. It promotes linguistic communication skills, which are essential for assessing the knowledge that allows us to understand the world around us and develop social awareness.

Building Blocks offers the possibility of incorporating active methodologies, using cooperative learning and thinking strategies, promoting personal and social skills for emotion management and the development of entrepreneurship in a flexible way. It attends to academic and professional orientation, whilst embracing equality and inclusion, all within the framework of the Sustainable Development Goals that we must keep focused on over the coming years.

Project keys SDG

SDG Commitment Establishes

the Sustainable Development Goals as a framework for learning that prepares students towards committed citizenship.

Developing thinking Proposes

strategies to stimulate reflection, “learning how to think” and the development of critical and creative thinking habits.

Cooperative learning Offers techniques to develop the skills that allow us to work together and efficiently in a diverse society.

Emotional education Offers emotional management tools to face the challenges of this complex educational stage.

Enterprising culture

Promotes entrepreneurial thinking in its three dimensions: personal, social and productive.

ICT Integrates the use of ICT in the learning process itself in a responsible, intelligent and ethical way.

Academic and professional orientation Helps students to get to know themselves, to understand the environment and to make decisions that allow them to confidently enter the labour market.

Assessment Incorporates strategies that allow students to participate in the assessment of their learning, analysing “what they have learned” and “how they have learned it”.

Linguistic Plan Develops communication skills both written and spoken and the tools needed to describe, present, instruct, comment, defend or refute ideas...

Our project the STUDENT’S book Using a skills-based methodology, the book presents content and activities that are adjusted to the curricular development of our community. It also allows us to express, in a creative and innovative way, our commitment to the Sustainable Development Goals. Our aim is to promote learning by combining the current science with the historical evolution of scientific knowledge in the fields of Physics and Chemistry.

THE DIGITAL PROJECT for teachers the web www.anayaeducacion.es The teacher’s website is a tool that facilitates and enriches teaching work.

With it, you can adapt the contents to the needs of the students through additional resources or reinforce the most relevant educational aspects: • Course plan, the Teacher’s Guide and project information.

• Diversity and inclusion, to meet the diversity of students’ motivations, interests and learning styles through:

- Key concepts and additional worksheets.

- Extension worksheets and competece development worksheets.

- Tasks, workshops and other resources.

• Assessment, a core value of the project, is supported through: -E valuation and activity generator: an activity bank which you can use to design tests for each topic.

- Predesigned assessment tests and records.

- Specific information.

- Assessment tools.

• Resource bank, which has resources to help you study, learn by playing, see virtual laboratories and simulations, videos, presentations, and access self-assessments and solutions, Language Bank, Create and more.

• Language Bank: created to further develop the four linguistic skills (speaking and writing, productive skills, and reading and listening, receptive skills), this new educational tool accurately supports the linguistic plan and can be used both by the teacher and the language assistant.

• Create: fun cross-curricular projects which contribute to integrating and exposing students to different curricular contents and developing their English skills. These projects show the students that what they’re learning isn’t just in the classroom, but found in everyday lives.

the teacher’s guide There is a Teacher’s Guide for each student book with the solutions to the activities, methodological guidelines, suggestions for applying the project keys, etc.

the digital book All Building Blocks books have a digital version.

You can download the entire book or download it by units, with all its resources or in its lighter version (without the largest digital resources), which allows offline and online use. The resources of each unit are grouped by type and allow direct access to the web resource bank and the Teacher’s Guide.

and for the s tudents?

Resource bank

at www.a n

ayaeduca cion.es: • Resourc es related to the pro ject keys.

• Feature d resourc e materia l.

• Resourc es for ea ch unit.

Digital b ook A digital version o f the textb be down ook that loaded in can full or by its resourc u nits; with es or a lig all hter versio heaviest d n (withou igital reso t th e urces).

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4 CHEMICAL REACTIONS ä Unit presentation

In this unit we will study the contents of the chemical changes block. The structure of the unit is based on macroscopic evidence of chemical changes and their characteristics and properties. At the beginning we will look at them from a phenomenological point of view, and then turn to the atomic description of chemical reactions. Graphic models are used to explain the information given by a chemical equation and related to the laws of chemical combination. The penultimate section moves on from the atomic to the macroscopic scale, and introduces the amount of substance in this way. Lastly, this unit tackles aspects related to the environment, such as acid rain, the anomalous greenhouse effect, the hole in the ozone layer and the tropospheric ozone.

ä Resources and materials In addition to the Student's Book and the Teacher’s Guide, the digital resources available on the Anaya website, chemical reaction simulations, laboratory equipment and search engines will be useful for studying this unit.

CC: core competencies, CLC: competence in linguistic communication, CMST: competence in mathematics, science and technology, CD: digital competence, CLL: learning to learn, CSAC: social and civic competence, SIE: sense of initiative and entrepreneurship and CAE: cultural awareness and expression.

Contents and competencies Unit content Opening pages • The study of transformations • SDG commitment

CLC CMST

Changes in the composition of substances • Chemical changes • Diversity of chemical reactions • Evidence of chemical reactions

CLC CMST CD CLL CSAC

Atomic theory of chemical reactions • Collision theory • Factors that affect the reaction rate

CLC CMST CD CLL SIE

Chemical equations

CLC CMST CD SIE

Laws of chemical combination and chemical equations • Law of conservation of mass • Law of definite proportions

CLC CMST CD CLL

Amount of substance • Amount of substance • Molar mass

CLC CMST CD CLL

Chemistry, environment and society • Environmental problems • Chemical industry

CLC CMST CD CLL CSAC SIE CAE

Science workshop • CO2 sinks • Chemical reactions with gaseous substances

CLC CMST CLL CSAC SIE

Review • Organising my ideas • Changes in composition • Atomic theory of chemical reactions • Representation of chemical reactions • Laws of chemical combination and chemical equations • Amount of substance • Chemistry and environment

CLC CMST CLL CSAC SIE

ä General suggestions Previous learning and possible difficulties Confirming a chemical change, identifying it and describing its characteristics are all dealt with in previous stages of the students’ learning. For this reason, we would expect them to be able to easily identify them. However, this unit will go one step further by studying chemical changes generically and not only in a specific context, such as metabolic processes or material degradation, which students already know how to describe qualitatively.

To reach this goal, we recommend that teachers emphasise the fact that this year’s content can be applied to phenomena they already know in order to describe them quantitatively in subsequent years.

In addition, this unit deals with methodological content that is key to learning about balancing chemical equations. Therefore, we recommend planning enough time for students to acquire this content through the activities proposed in a variety of formats.

Related tasks During the development of this unit, teachers will deal with the problem of climate change as a result of the anomalous greenhouse effect. The science workshop proposes a research project on an action that contributes to reducing this effect: carbon dioxide sinks. It may be helpful to relate this research work to the content addressed in other areas, from the point of view of a world economic strategy, focused on this purpose.

Values education As this unit lays the foundation for later chemistry studies, it must be approached with this in mind, and the need to build upon the acquired knowledge with new learning emphasised, thus fostering the learning to learn competence.

We recommend encouraging collaborative work as this directly influences the development of the social and civic competencies.

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Core competencies

SDG commitment

KEY PARTS SDG commitment • Goal: 14 • Targets: 6.1, 7.2, 13.1, 13.a

We recommend suggesting that students watch the video explaining SDG 14, which is available at anayaeducacion.es, before answering the proposed questions.

ICT The section ‘What you should know’ contains concepts that our students should know before starting the unit.

4

Linguistic Plan • Reading and listening (receptive skills) • Speaking and writing (productive skills)

Speaking An interview

CHEMICAL REACTIONS

5

In pairs, imagine one person is a journalist and the other an expert on climate change. Use the following information to ask and answer questions on how people can conserve and sustainably use the world’s oceans, seas and marine resources.

Reading and listening

For open ocean and deep sea areas, sustainability can be achieved only through increased international cooperation to protect vulnerable habitats. Establishing comprehensive, effective and equitably managed systems of governmentprotected areas should be pursued to conserve biodiversity and ensure a sustainable future for the fishing industry.

Chemistry and global warming

Developing thinking Techniques: • I see, I think, I ask myself • Associative analysis • C&R • The image • What makes you say that?

Organising my ideas: • Venn diagram • Outline • Systematic concept map Cooperative learning • Think and share with a partner • Puzzle • Prepare the task • 1-2-4 Enterprising culture • Taking risks (productivity dimension) Academic and professional guidance • Searching and analysing information ICT • Language Bank (Speaking) • Language Bank (Writing) • Videos and presentations: ‘Evidence of a chemical reaction: appearance of a gas’, ‘Evidence of a chemical reaction: appearance of a precipitate’, Evidence of a chemical reaction: change in colour’, ‘Formation of ammonia’, ‘Oxidation of an apple’, ‘Propane combustion’, ‘Carbon dioxide’, ‘What you should know’, ‘The amount of substance: the mole’ and ‘Let’s study!’

• Virtual laboratory: ‘Reagents, products and excesses’ and ‘Balancing chemical equations’ • And also: Interactive activities, videos and presentations to review and expand upon content Assessment • Review • Writing the portfolio

Global warming and chemical reactions are not only affecting our atmosphere, the impact is also polluting our oceans. For this reason, SDG 14 focuses on ‘life below water.’

Chemistry is the scientific discipline that deals with chemical transformations; the change of substances from one to another resulting from reactions. As in many other fields of study, what forms the core of chemistry nowadays is the result of many years of research and practical work. Centuries ago, the predecessor of chemistry was alchemy, a non-scientific study of matter with different aims, for instance, finding the elixir of immortality. Although alchemy did not evolve, it set the basis that allowed asking relevant questions, thus igniting the development of the field.

On a local level, we should make ocean-friendly choices when buying products or eating food derived from oceans and consume only what we need. Selecting certified products is a good place to start.

Making small changes in our daily lives, like taking public transport and unplugging electronics saves energy. These actions reduce our carbon footprint, a factor that contributes to rising sea levels.

Research laboratories are places where cutting-edge chemistry takes place. Some objectives encompass developing techniques to enhance the efficiency of chemical reactions that accelerate or slow down industrial processes, studying reactions that take place in the environment, as well as designing specific reactions that could impact entire societies.

We should eliminate plastic usage as much as possible and organize beach clean-ups. Most importantly, we can spread the message about how important marine life is and why we need to protect it.

Source: https://www.un.org/sustainabledevelopment/wp-content/ uploads/2018/09/14.pdf

Global warming could potentially jeopardise the existence of human beings, thus one of our biggest concerns. The origin of global warming takes place in the emission of considerable amounts of carbon dioxide to the atmosphere exceeding the limit that nature can absorb. A consequence of these emissions reflects on an increase in the average temperature of the planet. This situation has been taking place ever since industrial revolutions and has increased with the establishment and proliferation of industries all around the world.

What can we do to take of our oceans and seas?

We can use less plastic.

Writing An infographic

1 What is the difference between alchemy and chemistry?

2 What is the main point of the introduction?

6

3 Find two synonyms to the word ‘jeopardise.’

4 Name four different types of industries. Give an example of

Based on the previous information and on deeper research, create an infographic to inform people on specific actions they can take to conserve and sustainably use the world’s oceans, seas and marine resources.

BANK GE BANK LANGUA LANGUAGE BANK GE BANK GE BANK LANGUA LANGUAGE NK LANGUA BANK 107 BANK GE BA GE BANK LANGUA LANGUAGE NK LANGUA LANGUAGE NK BANK NGUAGE BA UAGE BA NGUAGE LA LANG

each.

106

LA

Opening pages Introduction There are several learning standards on this topic related to changes. The students’ understanding can be assessed through written activities, like those related to using models to interpret chemical reactions (collision theory) or to checking the law of conservation of mass. Other standards are empirical and experimental, such as recognising chemical reactions in simple experiments.

Due to this variety, we recommend combining experimental activities with explanations and written tasks in lessons related to this unit.

Answer key 1 Alchemy is a non-scientific study, whereas chemistry is.

2 Map the development of chemistry as a scientific field, its evolution, and the consequences of the abuse of it.

3 Threaten and hazard.

4 Car industry: Mercedes Benz Food industry: Nestle Electronics devices (laptops, tablets, phones) industry: Apple Clothing industry: Zara

5 Clarify the meaning of any word in the examples that students cannot

understand. Go word by word and ask students if they comprehend their meaning. Trend, ratio, proportion, significant, population density, tendency and side effects are essential words that students should learn in this activity.

The second task is to pay attention to the correct use of structures to generate the questions that the reporter will ask. Help students to adapt the structure to whatever they want to ask.

6 Ensure that students pick a topic that can be covered within an infographic.

Help students to clarify and select a ‘type of person’ to work with. Make sure that students do the research according to the topic they have chosen.

Furthermore, as sentences have to be short and concise, aid students in thinking of compelling sentences that can cover the message they want to convey. Monitor that the images selected add to the written information to achieve a clear message. Finally, give some examples as what colours, fonts and size of letters are convenient in each case.

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Unit

ä 1.1. Chemical changes

ä 1.3 Evidence of chemical reactions

As we have learned, there are changes in matter where substances do not change; in other words, no new substance appears. We call these physical changes. But there is another kind of change where some substances are transformed into different ones; we call these chemical changes:

At times, it is not obvious that a chemical change is taking place. Because physical changes might be taking place at the same time, it might not be easy to see the appearance of new substances. Some evidence of a chemical change is:

Chemical changes, also called chemical reactions, are those which cause new substances to appear.

Therefore, we say a chemical reaction has taken place when: • The substances that were present before the change combine with each other and, partly, disappear. These substances are known as the reagents of the reaction.

• Due to the combination of reagents, one or several new substances appear which were not present before the change.

These substances are the products of the reaction.

A chemical reaction is any process where one or more substances are transformed into one or more substances.

The reagents transform into the products.

• Change in the properties of the environment where the reaction takes place. The properties of these new substances are different. For example, a precipitate (solid substance of low solubility) can form as a result of the chemical reaction, or bubbling may appear, if the new substance is a gas (in other words, of a boiling temperature lower than that of the environment).

• Energy exchange between the substances which intervene in the chemical reaction and its environment. For instance, in the case of combustion reactions, this energy exchange is noticeable, but it is not so evident in all chemical reactions.

Evidence of a chemical reaction

4

ä 1.2 Diversity of chemical reactions

2

The synthesis of insulin takes place in the pancreatic cells. It is an in vivo reaction.

Entrance of Ca2+

ATP

Ca2+

3

or formation of substances in different state of aggregation. As in the previous case, if a gas is produced, a bubbling coming out of the solution will be observed.

3A

change in colour. The appearance of a different colour in the reaction reveals the presence of a new substance.

4 Chemical Gas

Insulin

Mitochondria

Light and energy in the form of heat

Substance of low solubility

Diversity of chemical reactions

Insulin

or formation of a precipitate. If the reagents are in solution, it might be that the new substance obtained has a lower solubility, so it will precipitate and this may be observed at first sight.

2 Presence 1

Depending on the purpose of the reaction, it can be interesting to consider them as natural reactions, when no anthropogenic factors intervene; artificial reactions, if they occur due to human actions; reactions in aqueous solution, when substances are dissolved in water; or in vivo, reactions, such as those that take place inside cells.

K+

When we notice the formation of bubbles in a glass of tap water, can we conclude that a gaseous substance has been produced as result of a chemical reaction?

1 Presence

As a result of a chemical reaction, we can obtain

There is an infinite number of chemical reactions and criteria to classify them; for example, depending on the number of reagents and products: if there is a single reagent which becomes two products, there is a decomposition reaction, and, on the contrary, if two or more reagents become one product, there is a synthesis reaction.

Glucose insulin

Changes in the composition of substances

4

Working with pictures

1 CHANGES IN THE COMPOSITION OF SUBSTANCES

Substance of another colour

reactions that cause a great energy exchange are easily detectable, as it is the case of combustion, which exchanges energy in the form of light and heat.

Understand, think, search…

1

Photochemical smog, which causes atmospheric pollution in many cities, is a web of chemical reactions which are produced due to anthropogenic reasons.

Graphic organiser. Chemical change has been defined as the opposite of physical change. But we have learned that some physical changes accompany a chemical change, although not all of them. Draw a Venn diagram to show this relationship between them.

Explain your diagram to the rest of the class.

2

I see, I think, I ask myself. When we take a jug of lemonade out of the fridge, we may notice the formation of a precipitate at the bottom of the jug. Can we conclude that a chemical reaction has taken place?

Observe the evidence, and write the questions that occur to you to answer the activity.

Check anayaeducacion.es for a resource on the evidence of chemical reactions.

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Developing thinking The resource ‘Graphic organiser: Venn diagram’ is available to students at anayaeducacion.es, which will help them learn about the characteristics of this tool and apply it effectively to answer activity 1.

They can also look at the document ‘I see, I think, I ask myself’ to learn about the basics for applying this thinking skill to answer activity 2..

ICT

Suggested methodology We start this unit by highlighting the differences between physical and chemical changes. Although students already know this content, here we ask them to systematically study them.

• The idea of chemical change related to the hypothesis of atomic theory and the definition of elementary substance as one that cannot be broken down into other substances, while a complex substance can be broken down, can be to introduce the content of this section. Highlighting that this unit will not only cover the decomposition and synthesis processes, but will also cover any type of chemical reaction.

• To make the content more accessible to students, draw on the kitchen, where there are physical processes like salt dissolving and water boiling, and chemical processes like chemical browning in stews, toasting bread, etc. Also highlight that, even though it is not always easy to differentiate a physical change from a chemical change, we can always find the answer by analysing the substances that are present before and after the process.

Answer key Working with pictures

Recommend that students watch the videos showing three types of evidence of chemical change: the formation of a gaseous substance, the formation of a precipitate and change in colour. Play these videos in the classroom and then discuss them as a group to ensure that students have correctly assimilated this content.

The aim is for students to link the described phenomenon with the solubility variation of gases in relation to temperature, so that they take into account that the appearance of bubbles does not always correspond to a change in state or chemical reaction in order to complete the graphic information.

Understand, think, search...

1 Use a simple graphic organiser that is useful for comparisons. A graphic solution to this activity could be the following:

PHYSICAL CHANGE

Appearance of substance in another state of aggregation.

Disappearance of substance.

Appearance of substance with another colour.

Energy exchange

Change in form.

Change in state of aggregation.

Changes in the density of a substance.

CHEMICAL CHANGE

2 Use the learning to think strategy ‘I see, I think, I ask myself’, where students will write what they

see (described in the activity outline), what they think (possible answers to the phenomenon of the appearance of the precipitate) and what they ask, or in other words, whether the appearance of the precipitate is evidence of a chemical change.

2

Unit

ATOMIC THEORY OF CHEMICAL REACTIONS

Not all substances react with each other when they come into contact.

Some do so really quickly, others more slowly and others do not react.

Furthermore, there are factors which influence whether a chemical change takes place or not and the rate at which it will happen. In this summary, we will learn the theory that explains, at an atomic scale, how chemical reactions happen and how quickly they do so.

The rate of a chemical reaction is defined as the variation of the amounts of the products obtained, or of the reagents which disappear, per unit time.

ä 2.1 Collision theory According to Dalton’s atomic theory, a chemical reaction involves a reorganisation of atoms. In order to understand this process, we must keep in mind the ideas of the kinetic theory of matter, according to which matter is formed by particles (atoms, molecules or ions) which are in continuous movement. Due to this movement, particles crash into one another and, in appropriate conditions, the particles of the reagents move apart and regroup to form the products of the reaction.

At times, the intention is to promote the formation of certain products that are beneficial to society, such as those obtained by the chemical industry; therefore, the rate of certain reactions is increased.

A chemical reaction takes place if the particles of the reagents crash into one another in an effective way, so that molecular bonds are broken which keep atoms together in the reagents, and new bonds are formed which give rise to products.

• Temperature. When temperature increases, the speed of particles increases, so the energy of the collisions that take place between them also increases, leading to a greater number of effective collisions and, accordingly, an increase in the reaction rate. When the temperature decreases, we get the opposite effect.

For these collisions to be effective, two conditions must be fulfilled: • The collisions between particles must have enough energy.

• The collisions must happen with the proper orientation.

Proper orientation of collisions

4

Remember that…

ä 2.2 Factors that affect the reaction rate There are extremely fast chemical reactions, such as explosions, and other slower ones, such as the oxidation of iron.

However, in the case of non-desired reactions, such as food decomposition, the opposite effect is sought, that is to slow down the chemical change.

In both cases, it is indispensable to know which factors influence the reaction rate. Some of them are:

From now on, every time we talk about elementary entities, we will be referring to the smallest unit formed by a substance, which can be an atom, a molecule or a group of ions.

Working with pictures Besides temperature and concentration of reagents, there is another factor which affects the reaction rate: the presence of catalysts. Look up information on these substances and explain why they are so important.

Give several examples and share your findings with the rest of the class.

Suggested methodology

• Concentration of reagents. In reactions that take place in solution, if the concentration of reagents increases, there will be a greater possibility of collisions between particles, and therefore, a faster reaction rate.

Factors which influence reaction rate

Effective collision

Molecules get closer with enough energy and proper orientation.

An effective collision is produced.

New bonds are formed giving rise to the molecules of the products.

Food decomposition reactions are faster at room temperature (right) than inside cooled chambers (left).

Non-effective collision

The concentration of reagent in the reaction on the right is higher than that on the left, and therefore, the reaction rate is higher.

Molecules get closer with enough energy but orientation is not proper.

Understand, think, search…

The collision is not effective.

Molecules of products are not obtained, in other words, there is no chemical reaction.

3

Graphic organiser. Create an outline where you connect the ideas of the kinetic theory of matter and Dalton’s atomic theory with the collision theory of chemical reactions. Write conclusions on the factors which influence the rate of chemical reactions.

4

Think and share with a partner. Reflect and answer these questions: a) Do you think pressure affects the reaction rate if the reagents are gases? b) Will a log of wood burn before the same mass in the form of splinters?

At anayaeducacion.es, there is a resource on the formation of ammonia and another one about the oxidation of an apple.

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Atomic theory of chemical reactions

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Developing thinking At anayaeducacion.es students will find the resource ‘Graphic organiser: Outline’ with which they can review the basics of applying this thinking strategy.

Cooperative learning Recommend the resource ‘Think and share with a p a r t n e r ’ to st u d e n t s , w h i c h i s ava i l a b l e a t anayaeducacion.es, so they can learn the basics for applying this cooperative learning technique and use it to solve activity 4.

ICT Resources on the formation of ammonia and oxidation of an apple are available so students can familiarise themselves with the bond breaking and forming processes and the factors that affect them.

One of the difficulties teachers may encounter when studying the collision theory comes from the fact that students have not, until now, thought about the conditions that lead to bonds breaking and forming in chemical reactions. Highlighting that a chemical reaction only takes place in specific conditions and between certain reagents can help introduce the topic. In addition, the incorrect idea that a chemical reaction is additive may arise. This means that students may believe that the molecules of the reagents join together to form larger ones.

• The stochastic and dynamic nature of chemical reactions when describing them at the microscopic scale must be introduced in order to understand the collision theory of chemical reactions. It is a good idea to subtly introduce this non-deterministic behaviour, where not all collisions lead to the formation of the molecules of products, and not all the molecules of reagents have the same energy value, but are distributed around an average value.

• Once the chemical reactions have been analysed based on collision theory, including the important considerations, it is easy to deduce the factors that affect the reaction rate.

Answer key Working with pictures Catalysts are substances that increase the reaction rate when they are present, and allow some very slow reactions, or reactions that require very high temperatures, to take place in more favourable conditions.

In some cases where there are several possible reactions, catalysts ensure that one particular reaction takes place. Some biologically-important catalysts are enzymes.

The picture shows an exhaust pipe catalyst for vehicles with an internal combustion engine.

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Understand, think, search...

3 Use a graphic organiser. Students are free to choose the type of outline and must link the following concepts: matter is formed by atoms; different chemical elements have different atoms; chemical compounds are formed by atoms of different elements; the particles that make up matter are in continuous movement, colliding with each other; a chemical reaction takes place when the collisions between molecules of the reagents have suitable energy and direction in order for the atoms to form different bonds, giving rise to new substances.

4 The aim is to encourage the exchange of ideas using the activity ‘Think and share with a partner’. It is expected that the answers include the fact that pressure does have a favourable effect on the number of collisions between molecules of gaseous reagents, and that the greater contact surface between oxygen and the wood, if it is in the form of splinters, increases the reaction rate.

3

Unit

CHEMICAL EQUATIONS

A chemical equation is the symbolic representation of a chemical reaction which contains quantitative and qualitative information.

Quantitative information refers to the number of elementary entities (atoms, molecules or ions) of reagents and products which intervene in the reaction. Qualitative information will be that which shows the state of aggregation of substances and the conditions in which the reaction takes place. A chemical equation is made up of: • Chemical formulas of the reagents separated by the ‘+’ sign, the symbol for chemical change (→8) and the formulas of products, also separated by the ‘+’ sign.

• Stoichiometric coefficients, which indicate the number of particles of each substance that intervenes in the reaction. If the value of the coefficient is one unit, it is not written.

To read the quantitative information that a chemical equation contains, it needs to be balanced. The number of atoms of each chemical element intervening in the process must be equal in both the reagents and the products. This is achieved by choosing the appropriate values for the stoichiometric coefficients, as shown in the charts on this page and the following one.

Balancing a chemical reaction We balance the reaction of iron sulphide (II) with oxygen to convert into iron oxide (III) and sulphur dioxide.

Without changing the chemical formulas of both reagents and products, we follow these steps:

REAGENTS Iron sulphide(II)

The elements that only appear in one reagent and one product are chosen and we balance their stoichiometric coefficients. First, the metals and then the nonmetals:

Oxygen

4

Balancing a combustion reaction For this type of chemical reaction, we will always follow this method. We will use propane combustion as an example. In this chemical reaction, propane combines with oxygen to form carbon dioxide and water. The reagents and products of the reaction are: In order to know the number of molecules of carbon dioxide, we take into account that all the carbon atoms of propane will end up forming part of carbon dioxide.

REAGENTS

Propane

Oxygen

The number of water molecules is determined by the number of hydrogen atoms of propane, which is eight. Therefore, four water molecules are produced.

Carbon dioxide

Water

Lastly, there are ten oxygen atoms in the products; therefore, there will be five oxygen molecules in the reagents.

Suggested methodology

Following this reasoning, we establish the stoichiometric coefficients: C3H8 + O2 8 3 CO2 + H2O

C3H8 + O2 8 3 CO2 + 4 H2O

C3H8 + 5 O2 8 3 CO2 + 4 H2O

PRODUCTS Iron oxide(III)

Sulphur dioxide

Then, we balance the simple substances, ending in H2 and O2. To do that, we count the number of atoms in the products and we balance the reagents:

REAGENTS 3 Ò 1 = 3 atoms C

PRODUCTS 1 Ò 3 = 3 atoms C

2 Ò 5 = 10 atoms O

2 Ò 3 + 1 Ò 4 = 10 atoms O

8 Ò 1 = 8 atoms H

2 Ò 4 = 8 atoms H

n.es there aeducacio chemical On anay balancing ane urce on prop is a reso and another equationsion. combust

Understand, think, search…

Therefore, the stoichiometric coefficients are: 2 FeS + O2 8 Fe2O3 + SO2

5 Write the chemical equation that corresponds to the 2 FeS + O2 8 Fe2O3 + 2 SO2

To avoid fractional coefficients we multiply all the coefficients by the denominator of 2 · (2 FeS + 7 O2 8 Fe2O3 + 2 SO2) 2 the fraction, although both expressions are valid: REAGENTS

PRODUCTS

1 Ò 4 = 4 atoms Fe

2 Ò 2 = 4 atoms Fe

1 Ò 4 = 4 atoms S

1 Ò 4 = 4 atoms S

2 Ò 7 = 14 atoms O

3 Ò 2 + 2 Ò 4 = 14 atoms O

2 FeS + 7 O2 8 Fe2O3 + 2 SO2 2

Work ing

with pictu res

Why do we coefficients avoid fractional stoichio in usefulininterprechemical equations? metric Are they tingthequalitat contained iveinforma in a chemic tion al equatio Look at the n? figures on these questio this page to answer ns.

balanced or not. Correct as necessary:

8 Balance the following chemical equations: a) Ca + H2O 8 Ca(OH)2 + H2 b) Fe (s) + HCl (aq) 8 FeCl3 + H2 (g) c) CH4 (g) + O2 (g) 8 CO2 (g) + H2O (g)

a) 4 NH3 + 6 O2 8 4 NO2 + 6 H2O b) 2 K + 3 H2O 8 2 KOH + 3 H2 c) 4 KMnO4 8 2 K2O + 4 MnO + 5 O2 d) Na2O (s) + H2O (l ) 8 2 NaOH (aq)

7 Which one of these chemical equations corresponds

to the reaction of nickel (II) chloride NiCl2, with sodium hydroxide, NaOH? Solutions for all the numeric activities at anayaeducacion.es.

112

a) NiCl2 + NaOH 8 Ni(OH)2 + NaCl b) NiCl2 +2 NaOH 8 Ni(OH)2 + 2 NaCl c) NiCl2 + Na2(OH)2 8 Ni(OH)2 + Na2Cl2 d) 2 NiCl2 + NaOH 8 2 Ni(OH)2 + NaCl

following description: Three dihydrogen molecules combine with one dinitrogen molecule to give two ammonia molecules’.

6 Indicate whether the following chemical equations are 4 FeS + 7 O2 8 2 Fe2O3 + 4 SO2

9

Chemical equations

PRODUCTS

Glucose fermentation is a type of decomposition reaction; glucose breaks down into ethanol and carbon dioxide. Look up the formula of the three compounds, write down the reaction that takes place and balance it.

Compare your solution with the rest of the class.

113

ICT Recommend that your students work with the virtual laboratory ‘Reagents, products and excesses’, which is available in the resource bank, to help them to symbolically understand what balancing a chemical equation entails.

They can also view the resource on ‘Propane combustion”, which illustrates the example used on this page.

Remind students that they can check the solutions of the numeric activities at anayaeducacion.es.

Continuing to study chemical reactions, here we show how they are represented symbolically: chemical equations.

• We start by describing the terms and symbols of the equations, to allow us to continue quantitatively interpreting a chemical equation at the atomic level. The following page of this section only focuses on balancing chemical reactions.

• Expected difficulties in this part of the unit can be related to both understanding the content and to doing the processes it involves. Therefore, start by highlighting that the dynamic process that takes place during a chemical reaction is represented sequentially in the chemical equation, separating the initial situation from the final one using an arrow.

• It should be noted that some students incorrectly relate chemical equations with algebraic equations and assume that the initial and final states of the chemical process correspond to the two parts of an algebraic equation.

• Therefore, we have separated the stages that must be followed to write a chemical equation (leaving out the balancing stage). Use the diagram included to write other chemical equations, like the reaction of solid aluminium with an aqueous solution of hydrochloric acid to form solid aluminium chloride with a release of gaseous hydrogen.

In addition, other difficulties can arise including the two described below. On one hand, the belief that false laws of conservation of the number of molecules, or elementary entities, of the reagents and products must be met. This difficulty is directly related to incorrectly relating chemical equations to algebraic equations.

On the other hand, some students cannot differentiate between stoichiometric coefficients and subscripts, which shows that incorrect connections are being made between the symbolic language of chemistry and the atomic meaning, both in the formula of a compound and the chemical reaction itself.

In order to overcome this difficulty, do activity 7.

Balancing chemical reactions can be tackled using a simple linear equation system, but we have chosen to not follow this method, rather opting for balancing by trial and error. We have done this for the following reasons: • We practise mental calculation.

• We help our student assimilate the formulae of the most commonly used chemical compounds.

• We keep the chemical equation present at all times so that they do not lose track of what they are doing.

• We help create a link between information at the atomic and macroscopic scale.

To make sure students successfully acquire a method, we recommend starting with the simplest case possible. The highest or lowest complexity of balancing equations lies in the number of different chemical elements that are involved. We can continue with the combustion of a simple hydrocarbon and systematically balance it, as we have proposed. Lastly, we can show examples where groups of atoms are involved, such as sulphate or carbonate ions, so that students learn to identify these groups of atoms in the formulation of salts, thus making it easier to balance substitution reactions.

Answer key Working with pictures The aim of this activity is for students to think about the meaning of a fractional coefficient when atomically interpreting a chemical equation because it is impossible to have part of a fundamental unit, and we must consider the whole unit. However, it is allowed when balancing chemical equations since, as we will see later, it is applied at the macroscopic scale where it does have a qualitative sense.

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3 CHEMICAL EQUATIONS

Unit

A chemical equation is the symbolic representation of a chemical reaction which contains quantitative and qualitative information.

Quantitative information refers to the number of elementary entities (atoms, molecules or ions) of reagents and products which intervene in the reaction. Qualitative information will be that which shows the state of aggregation of substances and the conditions in which the reaction takes place. A chemical equation is made up of: • Chemical formulas of the reagents separated by the ‘+’ sign, the symbol for chemical change (→8) and the formulas of products, also separated by the ‘+’ sign.

• Stoichiometric coefficients, which indicate the number of particles of each substance that intervenes in the reaction. If the value of the coefficient is one unit, it is not written.

To read the quantitative information that a chemical equation contains, it needs to be balanced. The number of atoms of each chemical element intervening in the process must be equal in both the reagents and the products. This is achieved by choosing the appropriate values for the stoichiometric coefficients, as shown in the charts on this page and the following one.

Balancing a chemical reaction We balance the reaction of iron sulphide (II) with oxygen to convert into iron oxide (III) and sulphur dioxide.

Without changing the chemical formulas of both reagents and products, we follow these steps:

REAGENTS Iron sulphide(II)

The elements that only appear in one reagent and one product are chosen and we balance their stoichiometric coefficients. First, the metals and then the nonmetals:

Oxygen

4

Balancing a combustion reaction For this type of chemical reaction, we will always follow this method. We will use propane combustion as an example. In this chemical reaction, propane combines with oxygen to form carbon dioxide and water. The reagents and products of the reaction are: In order to know the number of molecules of carbon dioxide, we take into account that all the carbon atoms of propane will end up forming part of carbon dioxide.

REAGENTS

Propane

Oxygen

The number of water molecules is determined by the number of hydrogen atoms of propane, which is eight. Therefore, four water molecules are produced.

PRODUCTS

Carbon dioxide

Water

Lastly, there are ten oxygen atoms in the products; therefore, there will be five oxygen molecules in the reagents.

6 The equations of the activity are:

Following this reasoning, we establish the stoichiometric coefficients: C3H8 + O2 8 3 CO2 + H2O

C3H8 + O2 8 3 CO2 + 4 H2O

C3H8 + 5 O2 8 3 CO2 + 4 H2O

PRODUCTS Iron oxide(III)

Sulphur dioxide

Then, we balance the simple substances, ending in H2 and O2. To do that, we count the number of atoms in the products and we balance the reagents:

REAGENTS

PRODUCTS

3 Ò 1 = 3 atoms C

1 Ò 3 = 3 atoms C

2 Ò 5 = 10 atoms O

2 Ò 3 + 1 Ò 4 = 10 atoms O

8 Ò 1 = 8 atoms H

2 Ò 4 = 8 atoms H

n.es there aeducacio chemical On anay balancing ane urce on prop is a reso and another equationsion. combust

Understand, think, search…

Therefore, the stoichiometric coefficients are: 2 FeS + O2 8 Fe2O3 + SO2

5 Write the chemical equation that corresponds to the 2 FeS + O2 8 Fe2O3 + 2 SO2

To avoid fractional coefficients we multiply all the coefficients by the denominator of 2 · (2 FeS + 7 O2 8 Fe2O3 + 2 SO2) 2 the fraction, although both expressions are valid: REAGENTS 1 Ò 4 = 4 atoms Fe

112

PRODUCTS 2 Ò 2 = 4 atoms Fe

1 Ò 4 = 4 atoms S

1 Ò 4 = 4 atoms S

2 Ò 7 = 14 atoms O

3 Ò 2 + 2 Ò 4 = 14 atoms O

2 FeS + 7 O2 8 Fe2O3 + 2 SO2 2

6 Indicate whether the following chemical equations are 4 FeS + 7 O2 8 2 Fe2O3 + 4 SO2

Work ing

with pictu

res Why do we coefficients avoid fractional stoichio in usefulininterprechemical equations? metric Are they tingthequalitat contained iveinforma in a chemic tion al equatio Look at the n? figures on these questio this page to answer ns.

balanced or not. Correct as necessary:

a) Ca + H2O 8 Ca(OH)2 + H2 b) Fe (s) + HCl (aq) 8 FeCl3 + H2 (g) c) CH4 (g) + O2 (g) 8 CO2 (g) + H2O (g)

b) 2 K + 3 H2O 8 2 KOH + 3 H2 d) Na2O (s) + H2O (l ) 8 2 NaOH (aq)

7 Which one of these chemical equations corresponds

to the reaction of nickel (II) chloride NiCl2, with sodium hydroxide, NaOH? Solutions for all the numeric activities at anayaeducacion.es.

2 NH3 + 3 O2 8 2 NO2 + 3 H2O

8 Balance the following chemical equations:

a) 4 NH3 + 6 O2 8 4 NO2 + 6 H2O c) 4 KMnO4 8 2 K2O + 4 MnO + 5 O2

a) In the equation 4 NH3 + 6 O2 8 4 NO2 + 6 H2O all the coefficients are divisible by two; therefore, we should write the equation like this: We then check that the equation is balanced:

a) NiCl2 + NaOH 8 Ni(OH)2 + NaCl b) NiCl2 +2 NaOH 8 Ni(OH)2 + 2 NaCl c) NiCl2 + Na2(OH)2 8 Ni(OH)2 + Na2Cl2 d) 2 NiCl2 + NaOH 8 2 Ni(OH)2 + NaCl

following description: Three dihydrogen molecules combine with one dinitrogen molecule to give two ammonia molecules’.

Understand, think, search...

5 2 H2 + N2 8 2 NH3

9

Glucose fermentation is a type of decomposition reaction; glucose breaks down into ethanol and carbon dioxide. Look up the formula of the three compounds, write down the reaction that takes place and balance it.

Compare your solution with the rest of the class.

Reagents

Element

Products

2·1=2

N

2·1=2

3·2=6

H

2·3=6

3·2=6

O

2·2+3·1=7

113

The equation is not balanced, as the number of oxygen atoms in reagents and products is different.

The balanced equation would be: 4 NH3 + 7 O2 8 4 NO2 + 6 H2O b) The equation from the activity is: 2 K + 3 H2O 8 2 KOH + 3 H2 We check that the equation is balanced: Reagents

Element

Products

2·1=2

K

2·1=2

3·1=3

O

2·1=2

3·2=6

H

2·1+3·2=8

The equation is not balanced, as the number of oxygen and hydrogen atoms in reagents and products is different.

The balanced equation would be: 2 K + 2 H2O 8 2 KOH + H2 c) In this case, the equation given is: 4 KMnO4 8 2 K2O + 4 MnO + 5 O2 We check that the equation is balanced: Reagents

Element

Products

4·1=4

K

2·2=4

4·1=4

Mn

4·1=4

4 · 4 = 16

O

2 · 1 + 4 · 1 + 5 · 2 = 16

The equation is balanced. d) Lastly, we have the equation: Na2O (s ) + H2O (l ) 8 2 NaOH (aq ) We check that the equation is balanced: Reagents

Element

Products

1·2=2

Na

2·1=2

1·1+1·1=2

O

2·1=2

1·2=2

H

1·2=2

The equation is balanced.

7 It is equation b.

8 The balanced chemical equations are: a) Ca + 2 H2O 8 Ca(OH)2 + H2 b) 2 Fe (s) + 6 HCl (aq) 8 2 FeCl3 + 3 H2 (g) c) CH4 (g) + 2 O2 (g) 8 CO2 (g) + 2 H2O (g)

9 This activity asks students to work on the productivity dimension, actively taking risks, of the key

‘Entrepreneurial culture’. The chemical formula of glucose is C6H12O6 and the formula of ethanol is C2H6O. Glucose fermentation can be written as: C6H12O6 8 2 C2H6O + 2 CO2.

64

4

Unit

LAWS OF CHEMICAL COMBINATION AND CHEMICAL EQUATIONS

Between 1789 and 1804, the laws of chemical combination were published with empirical laws that establish relationships between the mass of the reagents and of the products in a chemical reaction.

ä 4.1 Law of conservation of mass In 1789, the French scientist A. Lavoisier reached the conclusion that, in a chemical reaction, mass is neither created nor destroyed; only a transformation of substances takes place. This observation can be stated in the following way: In a chemical reaction, the sum of the masses of the reagents is equal to the sum of the masses of the products.

The atomic theory explains this empirical law, since a chemical reaction is only a reorganisation of atoms. No new atoms are created; the atoms of the reagents are organised in a different way to form other substances, the products of the chemical reaction. Thus, the total mass of the reagents will be equal to the total mass of the products (Part 1 of the chart on the next page).

With this example, we prove the relationship between the laws of chemical combination (law of conservation of mass and law

Part 1

4 NH3 + 5 O2 8 4 NO + 6 H2O

Atomic mass

No. atoms in reagents

Balanced chemical equation.

No. atoms in products

N

14 u

4·1=4

H

1u

4 · 3 = 12

H

6 · 2 =12

O

16 u

5 · 2 = 10

O

N

4 · 1 + 6 · 1 = 10

REAGENTS NH3

We check that the chemical equation is balanced. We add the average atomic mass data, which will be necessary later on.

4·1=4

NO

H2O

14 + 3 · 1 = 17 u

2 · 16 = 32 u

14 + 16 = 30 u

2 · 1 + 16 = 18 u

17 u · 4 = 68 u

32 u · 5 = 160 u

O2

30 u · 4 = 120 u

18 u · 6 = 108 u

In a chemical reaction, the proportion by mass of the reagents and the products is fixed and independent of the amount that reacts.

120 u + 108 u = 228 u

68 u + 160 u = 228 u

We can explain this empirical law by taking these facts into account:

• The number of elementary entities of each substance that intervenes in the chemical reaction is constant and is expressed by means of the stoichiometric coefficients in the chemical equation.

Suggested methodology

PRODUCTS We calculate the molecular mass from the average atomic mass.

Here the law of conservation of mass and law of definite proportions is presented, which were mentioned in the section about atomic models to introduce Dalton’s atomic theory.

We calculate the mass of each substance in the reaction from its molecular mass and stoichiometric coefficient.

We check that the law of conservation of mass is satisfied.

• The composition of each chemical substance is constant and expressed in its chemical formula.

• The average atomic mass is a characteristic of each chemical element.

The mass of a compound is obtained from the mass of the elements which make it up.

Part 2 NH3

O2

NO

H2O

68 u

160 u

120 u

108 u

From the molecular masses of the substances that intervene in the reaction, we calculate the proportion between them.

Review what is explained in Part 2 of the chart on the next page.

Proportion between reagents

Understand, think, search…

mNH3

10 Knowing the average atomic masses of hydrogen

12 In the combustion reactions of wood in a chimney, we

11 From your answer to the previous exercise, verify that

13

(1 u) and nitrogen (14 u), does the formation of ammonia (NH3) from dihydrogen (H2) and dinitrogen (N2) comply with the law of conservation of mass?

the law of definite proportions is satisfied if we know that 7.5 u of dihydrogen combine with 35 u of dinitrogen to obtain 42.5 u of ammonia.

obtain ashes. The mass of ashes is lower than the mass of burned wood. Why does this happen? Is the law of conservation of mass satisfied?

Explain the meaning of ‘empirical law’ and ‘theory’.

What is the difference between an empirical law and a theory? Give an example of each case to back your statement.

mO2

=

68 160

=

These proportions remain constant for any mass, therefore obeying the law of definite proportions.

Proportion between products mNO

17

mH2O

40

=

120 108

=

10 9

Repeat the calculations from the equation:

Proportion between reagents and products mNH3 mNO

=

68 120

=

17 30

;

mNH3 mH O 2

=

68 108

=

17 27

mO2 160 4 = = ; m NO 120 3

;

mO2 mH2O

=

160 108

=

40 27

On anayaeducacion.es there is a resource on the laws of chemical combination.

114

Laws of chemical combination and chemical equations

of definite proportions), and the information obtained from a chemical equation.

Ammonia (NH3) combines with oxygen (O2) to give nitrogen monoxide (NO) and water (H2O).

ä 4.2 Law of definite proportions Between 1794 and 1804, J. L. Proust established that, when two or more simple substances react to form a compound, the proportion by mass of the simple substances that reacted always had to be the same. This was verified by changing the masses of reagents in succession and checking that their proportion always remained constant.

4

The laws of chemical combination and chemical equations

2 NH3 +

5 O 8 2 NO + 3 H2O 2 2

115

Linguistic plan In relation to activity 13, it is important to remind students that the section ‘Linguistic plan’ is available at anayaeducacion.es, where they will find the information they need on how to write an expository text.

ICT At anayaeducacion.es you will find the virtual laboratory ‘Balancing chemical equations’ which can help students to apply the laws of chemical combination to chemical equations.

The connection between the description of a reaction at atomic and macroscopic scale must come from the realisation that the atoms of each element have a different mass and, therefore, so do the elementary entities of the different substances. This means we must introduce the concept of amount of substance as a quantity, as well as its unit: the mole. However, as a preparatory step and maintaining the atomic scale, these laws can be studied in atomic mass units. This preparatory step enables students to grasp ideas about proportions in amounts of elementary entities (just as they have been interpreting chemical equations until now) and proportions between the masses of the substances involved, before introducing the amount of substance and its unit: the mole.

Moreover, we believe that studying science is not the only important aspect. We also need to learn to do science and about science. Therefore, we will not just present how these quantitative studies are carried out on chemical reactions today, but we will also show how they were done at the beginning of this field by applying the basic laws of chemistry.

This approach has been used throughout the presentation of the different atomic models, as already mentioned, and the fundamental laws of chemistry have been used as the basis of experimental evidence that led to the development of the atomic theory. Once our students have learnt this, pick up this evidence again in the unit dedicated to chemical reactions, therefore repeating the outline followed until now: experimental evidence and model, thus highlighting the application of the atomic theory, and knowledge about the atom, in the quantitative study of chemical reactions.

Answer key Understand, think, search...

10 The balanced chemical equations is: 3 H2 + N2 8 2 NH3 We calculate the molar masses of all the substances using the data on atomic masses: H2

N2

NH3

2u

28 u

17 u

We calculate the mass of each substance involved in this reaction according to the information of the balanced chemical equation: H2

N2

NH3

3·2u=6u

1 · 28 u = 28 u

2 · 17 u = 34 u

The sum of the masses of the reagents is 6 u + 28 u = 34 u, which is equal to the sum of the masses of the products. The law of conservation of mass is fulfilled.

11 Using the masses of the previous activity, we establish the ratio between them and the masses of the substances given in this activity:

H2

N2

NH3

Activity 10

6u

28 u

34 u

Activity 11

7.5 u

35 u

42.5 u

The following relationships that confirm the law of definite proportions can be seen: m N2 28 u 35 u mH2 = 6 u = 7.5 u mNH3 34 u 42.5 u mH2 = 6 u = 7.5 u

12 The missing mass in the ashes corresponds to the combustion gases that form (carbon dioxide and water). The law of conservation of mass is fulfilled.

13 An empirical law accounts for a regularity observed through the experiment. By contrast, a theory

is the reasoned explanation, within a scientific paradigm, of that regularity observed in the empirical law. The laws of chemical combination are empirical laws and Dalton’s atomic theory explains them.

65

5

Unit

A chemical reaction does not take place between a few particles; the number that intervenes is enormous, therefore, it is not practical to use the atomic mass unit. For that reason, this will be quantified in a different way.

AMOUNT OF SUBSTANCE

ä 5.1 Amount of substance

Amount of substance and mass

The amount that measures the number of elementary entities of a substance is called amount of substance and its unit in the SI is the mole.

Calculate the mass of water, expressed in grams, that is obtained if 204 g of ammonia (NH3) react completely with oxygen, according to the following reaction. Check that the law of conservation of mass is fulfilled.

To calculate the mass of chemical substances intervening in a reaction, we start by its molar mass and the amount of substance of each one of them.

4 NH3

The quantity of grapes and chickpeas is the same; however, the mass of that quantity is different, since the mass of a grape is different from that of a chickpea.

One mole contains exactly 6.022 140 76 · 1023 elementary entities. This figure is called Avogadro’s number, NA.

Mass of a mole

ä 5.2 Molar mass

The value of molar mass of a substance numerically matches the molecular mass, or the mass of the formula unit, of that substance.

Substance

Molecular mass or formula mass/u

Molar mass/ (g/mol)

Au

196.97

196.97

KCl

74.6

74.6

NO2

46.0

46.0

To establish the relationship between the mass of a substance and the present amount of that substance, we use the molar mass.

N H O

n (mol) =

m (g) M (g/mol)

8

H2O

M (NO) = 14 + 16 M (NO) = 30 g/mol

M (H2O) = 2 · 1 + 16 M (H2O) = 18 g/mol

mO2

4 mol

m (g) g n mol

=

mlNH3 mlO2

6 mol

mNO = 30 g/mol · 4 mNO = 120 g

mNH3 mO2

=

mlNH3 mlO2

mH2O = 18 g/mol · 6 mH2O = 108 g

mNH3 mO2

=

160 g O2

From the stoichiometric coefficients and the molar mass of each substance, we calculate the masses of each substance to be able to establish the proportion by mass.

mlNH3 mlO2

We apply the proportion by mass to calculate the masses of the remaining substances from the mass of ammonia.

Data: m'NH3 = 204 g 68 g NH3

Suggested methodology

We calculate the molar mass of substances from their average atomic masses.

Stoichiometric coefficients indicate the proportion between reagents and products expressed in amount of substance.

g m (g) = n (mol) · M d mol n

Md

mNH3 = 17 g/mol · 4 mO2 = 32 g/mol · 5 mNH3 = 68 g mO2 = 160 g

mNH3

The numerical value of the average atomic mass equals the value of the mass in grams of a mole of atoms (molar mass).

NO

5 mol

n (mol) =

14 g/mol 1 g/mol 16 g/mol

PRODUCTS

M (NH3) = 14 + 3 · 1 M (O2) = 2 · 16 M (NH3) = 17 g/mol M (O2) = 32 g/mol 4 mol

Balanced chemical equation.

6 H2O

+

DATA: Molar mass N H O

O2

Remember that these proportions always remain constant. =

204 g NH3

68 g NH3

mlO2

120 g NO

mlO2 = 480 g

Mass, amount of substance and number of elementary entities

4 NO

14 u 1u 16 u

REAGENTS NH3

The molar mass, M, of a substance is the mass of one mole of that substance, in other words, the mass of 6.022 140 76 · 1023 elementary entities of said substance. Their units in the SI are kg/mol, although g/mol is used more often.

The molar mass enables calculations to be made at a macroscopic scale from combinations of units of atomic scale. The relationship between amount of substance, n, and molar mass, M, is as follows:

5 O2

+

DATA: Average atomic mass

The property of matter that represents the amount of substance is not mass, but the number of particles that make up a certain extent of substance.

As the mass of these particles is so small, the number of entities that make them up, for example, a gram of any substance is enormous. Moreover, this number will be different from one substance to another, as the elementary entities that make them up have different masses.

Amount of substance

4

Chemical reactions and amount of substance

=

204 g NH3

68 g NH3

mlNO

108 g H2O

mlNO = 360 g

204 g + 480 g = 684 g

=

204 g NH3 mlH2O

mlH2O = 324 g

360 g + 324 g = 684 g

We check that the law of conservation of mass is fulfilled.

For a mole of acetaldehyde (ethanal, C2H4O), we know that: M (C2H4O) = 12 · 2 + 1 · 4 + 16 · 1 = 44 g/mol 44 g of C2H4O

6.022 · 1023 molecules

1 mole of C2H4O

24 g of C

1.2044 · 1024 atoms C

In 1 mol of C2H4O there is 2 mol of C Multiplying by M (g/mol)

Multiplying by NA

4 g of H

In 1 mol of C2H4O there is 4 mol of H

2.4088 · 1024 atoms H

16 g of O

In 1 mol of C2H4O there is 1 mol of O

6.022 · 1023 atoms O

Understand, think, search…

14 Calculate the amount of substance present in 350 g of the following substances:

a) Potassium chloride, KCl

c) Sucrose, C12H22O11

b) Iron.

d) Ozone, O3.

15 Given the following equation, without balancing: N2 (g) + H2 (g) 8 NH3 (g)

On anayaeducacion.es there is a resource on the amount of substance quantity.

116

Give reasons for whether the following statements are true or false: a) 1 g of N2 reacts with 3 g of H2. b) 1 mole of N2 reacts with 1 mole of H2. c) 1 mole of N2 produces the same amount of NH3. d) 28 g of N2 react with 2 g of H2 to produce 50 g of NH3.

117

ICT The resource on ‘The amount of substance: the mole’ will strengthen the student’s knowledge acquired in these pages.

Here we introduce for the first time the concept of mole as the unit for the amount of substance, which is a quantity that relates the interpretation of a chemical reaction to the atomic and macroscopic scales. To emphasise this relationship, start with the atomic interpretation of the chemical reaction of the example on the odd page, asking the class to describe it out loud. Then ask the class how many oxygen molecules we would need in order for four ammonia moles to react, instead of four ammonia molecules, as given by the atomic interpretation. This activity makes the transition from the atomic scale to the macroscopic scale, and it gives us the opportunity to highlight that we must not meet a false law of conservation of the amount of material because in the example we have nine moles in the reagents and eight moles in the products.

In addition, another aim of this section is to master the concept of amount of substance, the value of the number of units covered by a mole (the Avogadro constant) and take into account that the same number of moles of different substances corresponds to different mass values, meaning that students must know how to calculate molar masses.

There are intrinsic challenges to understanding the mole. It is the unit of a quantity (amount of substance) that the students usually confuse with mass, given their tendency to quantify the amount of matter using mass. In addition, the quantity of the Avogadro number means that scientific notation must be used, which along with its own value, is an added difficulty.

Secondly, we introduce molar mass in this section. Once students have understood the meaning of the mole, it is relatively simple to conclude that the same amount of different substances will have a different mass. It is important to revise the concept of average atomic mass to use it to reach the molar mass of a chemical element and of a substance.

In this part of the presentation it may be useful to revise the measures in the box on the even page and the relationship between them.

Once the introductory activity has been completed and the meaning of molar mass and the amount of substance have been taught, cover step-by-step the outline provided on the left-hand page, as indicated in the text.

It is important to emphasise the fact that students must come up with their own strategy to solve the problem so as to avoid using ‘recipes’ that prevent them from adequately thinking about what they are doing. The aim is also for them to develop the ability to solve problems, which is a cornerstone of the scientific and mathematical competence.

Do activities 22 to 28 at the end of the unit once you have finished presenting the content of this section, in addition to doing the activities it provides.

Answer key Understand, think, search...

14 To answer the question, students must calculate the molar masses of the substances using the average atomic masses.

Atomic masses Potassium

39.1

Iron

55.8

Carbon

12.0

Hydrogen

1.0

Chlorine

35.5

Oxygen

16.0

From the average atomic masses and the chemical formula of the substances, we calculate the molecular masses: Molecular masses (g/mol) KCl

74.6

Fe

55.8

C12H22O11

342

O3

48

Once we know the molar masses (M), we calculate the amount of substance (n) in the mass measurement given in the activity, m = 350 g, using the relationship between these two quantities: n (mol) =

66

m (g) g m Mc mol

We get the following answers: a) nKCl = 4,7 mol b) nFe = 6,3 mol c) nC12H22O11 = 1,0 mol d) nO3 = 7,3 mol

15 The balanced chemical equations is: N2 + 3 H2 8 2 NH3 a) The statement is false because it establishes a proportion between masses that does not correspond to the stoichiometric proportion. b) False. The proportion between the reagents, in the amount of substance, is not 1:1 but 1:3, as shown in the balanced chemical equation. c) False. A mole of N2 produces double the amount of ammonia. d) False. By calculating the molar masses of the substances and using the ratio between the amount of each substance, we find that 28 g of dinitrogen react with 6 g of dihydrogen, and 34 g of ammonia is obtained.

6

Unit

Chemistry has a great impact on people’s quality of life, as it provides knowledge about new substances with all kinds of applications and contributes to the search for solutions to severe environmental problems.

CHEMISTRY, ENVIRONMENT AND SOCIETY

ä 6.1 Environmental problems Some of these problems take place in the atmosphere as a result of gas emissions in chemical reactions.

Acid rain In some industrial areas, gases are emitted, such as sulphur oxides and nitrogen, which move through the atmosphere and react with the atmospheric water vapour giving rise to corrosive acids, such as sulphuric (H2SO4) and nitric (HNO3) acids. When this solution of gases in water precipitates in the form of rain (called acid rain), it has catastrophic effects.

Besides destroying buildings and historical monuments in towns, it also has a harmful effect in the flora and fauna of forests, rivers and lakes.

Anomalous greenhouse effect The presence of carbon dioxide, CO2, in the Earth’s atmosphere keeps the temperature in our planet within certain values which enable life as we know it. This phenomenon, explained in the figure below, is known as the greenhouse effect.

The dimensions of our daily life that are influenced by the development of chemistry are numerous, from water purification to the most advanced materials which are part of electronic devices, to polymeric fabrics and materials, car bodies and many more.

Most infrared radiation is absorbed by the greenhouse gases

Part of the solar radiation is absorbed by the Earth’s surface and it warms it

The Earth’s surface emits infrared radiation

Greenhouse gases, such as CO2, present in the atmosphere, absorb part of the infrared radiation emitted by the planet and keep this radiation from dissipating outwards, contributing in this way to keep the average temperature of the Earth stable. If the atmosphere did not exist, the Earth’s surface would reach very high temperatures during the day and would be too cold at night, making the existence of life impossible.

16

Associative analysis. Besides limiting the use of CFCs, there is another reason behind the reduction of the hole in the ozone layer. Look up information and share it with the rest of the class. How could this situation be improved without harming the planet?

17

Explain the differences between tropospheric and stratospheric ozone. Are there any differences between one molecule and the other?

18

Explain why CO2 is necessary in our atmosphere.

What are the effects of the anomalous greenhouse effect? Search how it relates to goal 13.1 and think of how it could be sorted. Which actions are being carried out at the moment?

19

Look up information about the chemical product used to purify water and its cost. Write up a report and include a conclusion on its use with goal 6.1.

20 The development of the chemical industry is

accompanied by high pollution levels of water, air and soil. Many companies have tried to reduce this negative effect for some time, but it is very difficult due to the high economic costs and the complex adaptation of infrastructures. Look up information about a company that has managed to adapt to the goals established by the UN. Which measures have they adopted? Do you think it was easy?

In teams, design an action plan for any company that has not done this.

21

From what you have learned in the previous exercise, which university degrees and professional training could you study in order to work in the chemical industry?

At anayaeducacion.es there is a resource on the importance of CO2 in the atmosphere.

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We end this unit on chemical reactions by talking about some of the aspects related to the environment and the chemical industry.

Evolution of the ozone layer during 2019.

Understand, think, search…

Part of the radiation that reaches the Earth from the Sun is reflected and another part is absorbed; therefore, the Earth heats up and, in turn, emits infrared radiation, as a result of being at a specific temperature.

Chemistry, environment and society Suggested methodology

Effects of acid rain in a forest.

ä 6.2 Chemical industry One of the main goals of this industry is the transformation of raw matter into other products which, in turn, will be the raw matter for an infinity of processed products.

Atmosphere

Earth

On the other hand, since the Industrial Revolution, the presence of ozone in the lowest layer of the atmosphere, the troposphere, has been observed. This comes as a result of the emissions of nitrogen oxides and volatile organic compounds from the industry and motor vehicles. This tropospheric ozone is a pollutant, harmful to health and the environment.

This greater amount of CO2 means that infrared radiation is retained in excess, which in turn provokes an increase in the average temperature of the atmosphere shown, for instance, with an increase in the frequency and intensity of hurricanes and cyclones. These phenomena are part of what we call climate change, devastating effects on our planet.

The greenhouse effect

Part of the solar radiation is reflected by the Earth and the atmosphere

In the last decades of the past century, a hole in the ozone layer was detected, caused by the presence in the stratosphere of certain gases from human activity: the CFCs. Currently, environmental legislation has set strong limits on the production and use of these gases, and the hole in the ozone layer has been considerably reversed.

In recent decades, the amount of CO2 present in the atmosphere has noticeably increased. This is because the carbon cycle has been altered by using oil and coal as sources of energy in chemical combustion reactions.

The Sun

4

Stratospheric and tropospheric ozone Ozone is a molecule that consists of three oxygen atoms, O3, and forms a layer at about 60 km above sea level in the stratosphere. Ozone absorbs a part of the solar radiation that is harmful to health, ultraviolet radiation.

In this process, the ozone molecule breaks down into dioxygen, O2, and monoatomic oxygen, O. The special characteristic of this dissociation is that it is reversible, in other words, ozone can form itself again nearly at once. Therefore, stratospheric ozone makes up the ozone layer, which is kept intact despite ultraviolet radiation.

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ICT The resource on ‘Carbon dioxide’ is available at anayaeducacion.es, which can be used to emphasise to students the importance of this gas, which is essential for life.

Developing thinking We recommend that students look at the resource ‘A ss o c i a t i ve a n a l ys i s ’ , w h i c h i s ava i l a b l e a t anayaeducacion.es, to learn about the basics for applying this thinking skill to answer activity 16.

Linguistic plan We suggest recommending that students look at the ‘Linguistic plan’ section of the resource bank before answering activity 17. Here they will find the i n fo r m at i o n t h ey n e e d o n h ow to w r i te a n argumentative text.

SDG commitment At anayaeducacion.es there are videos relating to goals 13.1 and 6.1. Watching them will help students answer the questions in activities 18 and 19.

Academic and professional guidance We suggest using activity 21 to search for and analyse information related to the academic situation linked to the content addressed in these pages.

• Present acid rain as a global environmental problem, that is to say, not a local one, which has already been largely overcome through the elimination of sulphur emissions, which resulted from fuel desulphurisation.

• The greenhouse effect is addressed through the description of the natural phenomenon and through the global environmental problem caused by its anomalous aspect. In order for students to understand the greenhouse effect, they must be able to identify three types of radiation. In the current curriculum, the subject block on waves does not appear until baccalaureate. However, students are familiar with the different types of radiation in their day-to-day surroundings (infrared in remote controls, ultraviolet in sun care cosmetics), so introducing infrared radiation should not pose a problem. To help students better understand the phenomenon, work with the picture on the even page.

• The consequences of the anomalous greenhouse effect on climate is a current issue that students know about.

• We then show the problem of the hole in the ozone layer. It is common to see that they make incorrect conclusions about the causes of the hole in the ozone layer because some students tend to think that this problem is caused by greenhouse gases. Differentiating the causes of these two global environmental problems must be one of the aims of this part of the subject. To do this, show the evolution over time of both problems and the solutions that have been implemented in these cases. It is a good idea to highlight that the hole in the ozone layer is an environmental problem that has been addressed from a legislative point of view, with strong agreement. Conversely, the solution to climate change has been a change in the world’s energy model, for which there is currently no agreement on effective measures.

• End the presentation of environmental problems by addressing pollution by the tropospheric ozone.

Highlight the difference between the benefit and damage that the same substance can cause depending on its location.

• Lastly, different aspects in which the chemical industry is involved are mentioned, some of which, including water purification, are well-known to the students.

Answer key Understand, think, search...

16 One of the causes behind the reduction in the hole in the ozone are nitrogen oxides and compounds with bromine which are used as fertilisers. The actions that reduce the use of these substances will benefit the planet. For more information, students can look at the Ministry for Ecological Transition web page related to emissions into the atmosphere.

17 This activity aims to highlight the fact that there is no difference between the molecules, and the

substance is the same. This idea can be broadened by comparing carbon dioxide from a chimney in a thermal power plant and carbon dioxide produced by living beings through aerobic respiration.

18 This activity checks that students have understood that the average temperature of the planet is

related to the composition of the atmosphere. Delving deeper into this idea, and taking into account the target indicated in the activity, the aim is for students to relate the temperature increase to the occurrence of very high-energy atmospheric phenomenon (hurricanes, storms and cyclones) and effects on sea level, and inland water and oceanic water levels in a solid state, and how these directly affect people’s lives. The activity also aims to promote reflection about the

67

measures that can be taken. Similarly, we suggest relating this activity to the research project of the unit’s ‘Science workshop’.

19 Chlorine oxides are used to purify water. The precursor substances of these compounds can be:

hydrogen chloride, chlorite and sodium chlorate. In this regard, students can look at the consolidated text of 1 August 2018 of the Decree of the Ministry of Health, Social Services and Equality SSI/304/2013, of 19 February, on substances for purifying water intended for water production for human consumption. The cost of the chlorine oxide precursors is low and affordable (bleach or water treatment tablets, among others).

20 For this activity students can look at the United Nations business website (https://business.un.org/

en/browse/partnership_stories), which shows business actions related to the Sustainable Development Goals.

21 Vocational training courses in chemistry that focus on working in the industry are Diploma in

Chemical Plant Technician, Advanced Diploma in the Manufacture of Pharmaceutical, Biotechnological and Related Products, and Advanced Diploma in Industrial Chemistry, as well as university degrees in Chemical Engineering, Industrial Engineering, Materials Engineering, among others.

Unit

SHOP SCIENCE WORK

Research project CO 2 SINKS

CHEMICAL REACTIONS WITH GASEOUS SUBSTANCES

Introduction The increase in the amount of carbon dioxide in the atmosphere has a direct relationship with the increase in the average temperature of the planet. The most obvious and known cause of this increase in carbon dioxide emerges as a result of the combustion of oil and coal utilised in the transformation of chemical energy into electrical energy (goal 13.a).

However, there are other causes linked to the increase in carbon dioxide in the atmosphere, such as the increase in the world population.

Approaching the problem The presence of gas in a chemical reaction, such as a reagent or product, changes the pressure of the reacting mixture. The difference between this pressure and the atmospheric pressure makes it possible to have proof of the reaction.

NaHCO3(aq) + CH3COOH(aq) 8 CO2(g) + NaCH3COO(aq) + H2O(l ) [1] Sodium bicarbonate

2. Could chemical reactions be developed where CO2 was a reagent and thus reduce its presence in the atmosphere?

Puzzle

Laboratory equipment necessary perform the experiment.

Divide the class in groups of three. Each person will research one of the following areas, trying to answer the corresponding questions. Use bibliographies and references provided by the teacher.

1 There will be an exhibition in the school with the infographics of the work groups.

2 Organise a round table for each

area to explain the conclusions. All classmates will elect the members of the round table.

3

C&R. Each participant who follows the round tables will write an article which summarises the positions and conclusions drawn.

Discussion of results Meet the members in each group who have been researching the same area and share your answers to the questions. Then, write a report for your area.

to

CO2 sinks

Our proposal Pour the vinegar (which contains acetic acid) into the plastic bottle and introduce the sodium bicarbonate into the balloon. Carefully, cover the bottle with the balloon and pour the bicarbonate inside.

Observe the increase in volume of the balloon.

The first part of this science workshop consists of a research project which aims to make students think about the nature of CO2, its origin and its reactivity.

Materials • One 1.5 L flexible plastic bottle • One balloon • Around 100 cm3 of 6° vinegar • 8 g of sodium bicarbonate • 7 g of sodium hydroxide flakes

• Area 2. Artificial CO2 sinks. Can climate change be reversed? Is it enough to reduce the emissions of greenhouse gases? What are artificial CO2 sinks?

• Area 3. Autotrophic nutrition. Natural CO2 sinks. What is the carbon cycle? What is autotrophic nutrition? Which living beings carry it out?

Are they considered carbon sinks? Is there any action to promote this way of eliminating carbon dioxide?

[2]

Next, remove the balloon and add the sodium hydroxide. Screw the bottle cap and shake it, to boost contact between the carbon dioxide and the sodium hydroxide which is dissolving in the water. Observe the change in shape of the bottle.

• Area 1. Impact of overpopulation. What has been the trend in the number of inhabitants of the planet in the last two centuries? How are the population’s habits? What is the impact of overpopulation in climate change? Does it affect lifestyle?

Presenting your work

Sodium acetate

Figure out, how to carry out each one of the reactions so that the difference in pressure before and after the chemical change is obvious. Observe the list of materials we suggest.

Objective Procedure

Acetic acid

CO2 (g) + 2 NaOH (aq) 8 Na2CO3 (aq) + H2O (l )

3. In which natural process is CO2 a reagent and not a product of the reaction? Could this be the case with industry?

Research the so-called CO2 sinks and draw conclusions.

Research project

Prepare the task Your proposal We will carry out two chemical reactions, one where carbon dioxide is obtained as the product of the reaction [1] and another one in which this gas is one of the reagents of the reaction [2].

1. Could the air that human beings who inhabit this planet exhale in the breathing process influence this fact? Look up the most well-known causes of climate change.

Coral reef in the ocean that serves as a natural CO2 sink.

Science workshop

4

PRACTICAL WORK

Guidelines • The masses of reagents that we show in the method exceed the stoichiometric amounts to ensure an adequate reaction rate.

• Alternatively, the bottle can remain open in the first reaction, without using the balloon, so that the carbon

Conclusions Lastly, create an infographic with the pros and cons of each area to address actions related to the SDGs you have been working on.

dioxide produced fills the space in the bottle and comes out.

• To ensure this gas has displaced all the air that was inside the bottle, you can introduce a lit match and observe how the flame goes out.

Draw conclusions...

1

1-2-4. Work with your team and answer the following questions:

c) What is the meaning of the symbols in brackets in the chemical equations on this page?

b) Which effect is observed in the bottle when the second reaction takes place? Why?

d) Part of the reagents has not reacted. How do we know this?

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120

SDG commitment At anayaeducacion.es there are videos relating to goal 13.a.

Cooperative learning

It is common for current news outlets to subliminally put forward the idea that carbon dioxide is in itself a toxic substance since it damages the planet as a whole because it is a greenhouse gas. The last section of this unit shows that the effect of carbon dioxide is not in itself toxic, but the excessive accumulation of this gas in the atmosphere is harmful. The first introductory question to this research project aims to trigger the students’ critical part, as the goal is to compare the idea of the effects of carbon dioxide with the natural origin of this substance, making them reflect on the balance that this gas has on regulating the planet. In addition, the introductory paragraph before the question shows another of the big and controversial challenges of our time: overpopulation.

Apply the ‘Puzzle’ technique to do the research project since it allows students to be involved in their learning and participation in the learning of the class as a whole. It improves their performance and coexistence in class.

The second and third introductory questions aim to focus the research topic of this project, which revolves around the reactivity of carbon dioxide in certain conditions to thus propose complementary measures for reducing carbon dioxide emissions, where carbon dioxide is a reagent that disappears in chemical and biological reactions that are studied as sinks for this gas.

The techniques ‘Prepare the task’ and ‘1-2-4’ can also be applied to developing practical work and drawing conclusions, respectively. You will find explanations for these techniques at anayaeducacion.es.

Propose the project using the ‘Puzzle’ technique to make students share their thoughts with the rest of the work group and with students in other groups. We suggest gathering the conclusions in an infographic, so it would be a good idea to coordinate part of the work with the Art Department. Other formats for the conclusions of each group can be proposed, such as videos (in coordination with the English Department, which could assess the oral presentation) or posters containing quantitative information (in coordination with the Maths Department).

Developing thinking Students can look at the explanatory document of the technique ‘C&R’, the application of which we propose to answer activity 3 of presenting your work.

Presenting your work Conclusions can be shared as suggested in the text through a round table. In this case, we suggest proposing the activity as interdisciplinary work, where the English department assesses participation in the debate of the student’s in the round table and the audience. Alternatively, a simplified version of the activity can be proposed in the student’s second language study and it can be coordinated with the corresponding department.

Practical work Chemical reactions with gaseous substances Similarly to the rest of the practical work in this book, the work is set after the students reflect on how to carry out the laboratory practice. In this case, the students’ reflection is drawn from the list of materials necessary to do the practical work. It is common for students in year three of secondary school to know the chemical reaction of acetic acid with sodium bicarbonate and the release of carbon dioxide, but it is less common for them to know the reaction of this gas with sodium hydroxide.

The aim of this experiment is to observe the effects of pressure on the appearance or disappearance of a gaseous substance, the effect it has on the pressure difference between the inside and outside of a container with deformable sides and experiment with a transformation reaction of carbon dioxide to relate it to the research project of the previous page.

To broaden information on these experiments, students can look at the work of Tomás-Serrano, A. and Hurtado-Pérez, J. in Revista Eureka sobre Enseñanza y Divulgación de las Ciencias 15 (3), 3401, 2018.

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Answer key Draw conclusions…

1 a) The technique ‘1-2-4’ for individual, pair and group sequential work is proposed for this activity.

A reduction in volume is observed since the pressure inside the bottle reduces as a gaseous substance is consumed as a reagent. The explanation offered by KMT are: as the amount of gas reduces, the number of collisions of gas molecules against the inner walls of the container decrease, and the container deforms reducing its volume, because the pressure outside remains constant.

b) The symbols refer to the state of aggregation (s, solid; l, liquid, and g, gas) or to the solution of the substance in water (aq). c) One way of knowing that part of the reagents has not reacted in the case of the first reaction is to stir the bottle again and see that gas appears in the balloon, once we have released the gas that formed before.

r to choose Remembe for your portfolio.

resources from

this unit

Unit

REVIEW

ORGANISING MY ideas

Changes in composition

Hierarchical concept map

1 Copy the concept map in your notebook, or into an app to prepare concept maps, and do the following: a) Fill in the missing words. b) Explain why the word ‘molecules’ always has an alternative name in the concept map. To do this, think about the type of substances which are not molecular. c) Include a new branch in the indicated place in the concept map (1) to show which kind of change a chemical change is in relation with the composition of matter. d) From the branch in the previous activity, include which ones are pieces of evidence that show a chemical change is taking place.

e) Include in the map, from the place indicated (2), which other symbols can be displayed in a chemical equation.

1 What does it mean that the nature of matter is altered in a chemical change? Define in your own words the expression nature of matter.

f) From the law of conservation chart, indicate the mathematical way of expressing this law.

2 When vinegar and bicarbonate come into contact with each other, a gas is released, carbon dioxide, and sodium acetate and water are formed: a) Indicate the reagents of the reaction. b) Indicate the number of products of this reaction.

g) Indicate the relationship between amount of substance and mass in your concept map. To do this, include a branch in the place you consider appropriate. h) Based on orientation, illustrate with a drawing, and include it in the map, an effective collision and another one which is not effective. i) Include in the concept map the constant that connects the number of elementary entities with the amount of substance expressed in mole.

Chemical reactions

are represented by means of

are

Equations ? .................................

(1)

4 There are chemical reactions for which the main application is energetic, as a great amount of energy is released during their development. Give an example and explain which environmental problem is associated with them.

obey

Changes

in which we find

Law of conservation ? .........................................

in which the

Law of ? .........................................

Coefficients ? .................................

Molecules or ? .................................

Chemical formulas

of

6 Is collision theory compatible with the law of conservation of mass? Both of them explain certain aspects of the chemical reactions, but do they make use of the same scale? Explain your answers.

of

Reagents

Collide

7 The following table displays the masses of two substances while a chemical reaction takes place over time:

Number of Molecules or ? ................................

de

with enough

with proper

Energy

Orientation

and

which are expressed in the unit of amount of substance

? ...........................

Mole

of

Mass A/g

7,5

3,75

2,5

1,88

Mass B/g

1,7

3,4

6,8

13,6

Time/min

1

2

3

4

giving rise to

a) Are substances A and B, reagents or products of the reaction? Justify your answer.

Molecules or ? .................................

b) Graph the data of mass against time, and indicate if this is a linear relationship.

Solutions for all the numeric activities at anayaeducacion.es.

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8

Review

The image. Explain what this represents:

What similarities and differences are there between the previous representation and the following one?

The activities that require calculations and graphs to answer them will be provided and developed in the answer key included at anayaeducacion.es.

9 How does temperature affect the rate of a chemical reaction? Use the collision theory and kineticmolecular theory on the temperature and the average kinetic energy of particles.

Representation of chemical reactions

Atomic theory of chemical reactions 5 Do all collisions that take place between the reagent particles cause them to break? Which factors does a collision depend on to be effective?

(2)

which give us information about the

3 Indicate whether the following statements are true or false and explain why: a) Energy is released in all chemical reactions. b) Chemical reactions only occur naturally in living organisms. c) In a chemical reaction, reagents and products can be in different states of aggregation. d) Chemical reactions which take place in nature create an environmental problem.

4

c) From the previous chart, indicate in which time interval the rate of the chemical reaction is greatest. What do you base your answer on?

Connect this observation with the collision theory.

Organising my ideas

10 One student balances this chemical equation: NO + O2 8 NO2 as follows: NO + O2 8 NO3 Is what he has done right? Why?

11 Balance the following chemical reactions: c) NH3 + H2SO4 8 (NH4)2SO4 a) Al + O2 8 Al2O3 b) SO2 + O2 8 SO3 d) Fe2O3 + H2 8 Fe + H2O 12 Write all the information you can obtain from the following balanced chemical equation:

1 This activity can be used as samples for the students’ portfolio.

3 Cl2 (g) + 2 Fe (s) 8 2 FeCl3 (s)

13 Use this table to verify that the reaction in the previous exercise is balanced.

Element

Atoms in reagents

Atoms in products

Cl

a) In this activity students must organise the information by filling in the gaps in the diagram.

Fe

Chemical reactions

123

Assessment The preparation of a ‘Portfolio’ is a self-assessment proposal that allows students to think about the processes they have performed to acquire this learning.

are represented by means of Chemical equations

Developing thinking The ‘Hierarchical concept map’ allows students to organise and understand ideas about chemical reactions in a meaningful way, and to see the cognitive structure of the content to be learnt.

(1)

obey

Changes

in which we find

Law of conservation of mass

in which the

Law of definite proportions

(2) Stoichiometric coefficients

ICT We suggest reminding students that they can check the solutions of the numeric activities at anayaeducacion.es.

are

Molecules of elementary entities

Chemical formulas

which give us information about the

of

of

Reagents

Number

Collide

of Molecules of elementary entities

of

with enough

with proper

Energy

Orientation

and

which are expressed in the unit of amount of substance

Mole

giving rise to

Products

of

Molecules of elementary entities

b) Substances can also be formed by crystals or atoms. The expression ‘elementary entities’ refers to this. c) The diagram is made bigger by including: Changes in which the composition of matter is changed. d) The diagram is made bigger by including: Change of colour, appearance of a precipitate, bubbling, energy exchange in the form of light and heat. e) The diagram is made bigger by including: other symbols that indicate the state of aggregation of substances. f) ∑mreagents = ∑mproducts. If students do not know the summation symbol, write a generic reaction (A + B 8 C + D) and the law is expressed as a function of the generic substances. g) The ‘mole’ square can be linked to a new one containing the word ‘mass’ through the concept of ‘molar mass’. h) Include drawings like those used in the unit linked to the ‘orientation’ box. i) From the ‘mole’ box, include the Avogadro constant using the link ‘which contains as many units as’.

69

r to choose Remembe for your portfolio.

resources from

this unit

Unit

REVIEW

ORGANISING MY ideas

Changes in composition

Hierarchical concept map

1 Copy the concept map in your notebook, or into an app to prepare concept maps, and do the following: a) Fill in the missing words. b) Explain why the word ‘molecules’ always has an alternative name in the concept map. To do this, think about the type of substances which are not molecular. c) Include a new branch in the indicated place in the concept map (1) to show which kind of change a chemical change is in relation with the composition of matter. d) From the branch in the previous activity, include which ones are pieces of evidence that show a chemical change is taking place.

e) Include in the map, from the place indicated (2), which other symbols can be displayed in a chemical equation.

1 What does it mean that the nature of matter is altered in a chemical change? Define in your own words the expression nature of matter.

f) From the law of conservation chart, indicate the mathematical way of expressing this law.

2 When vinegar and bicarbonate come into contact with each other, a gas is released, carbon dioxide, and sodium acetate and water are formed: a) Indicate the reagents of the reaction. b) Indicate the number of products of this reaction.

g) Indicate the relationship between amount of substance and mass in your concept map. To do this, include a branch in the place you consider appropriate. h) Based on orientation, illustrate with a drawing, and include it in the map, an effective collision and another one which is not effective. i) Include in the concept map the constant that connects the number of elementary entities with the amount of substance expressed in mole.

Chemical reactions

are represented by means of

are

Equations ? .................................

(1)

Changes

in which we find

4 There are chemical reactions for which the main application is energetic, as a great amount of energy is released during their development. Give an example and explain which environmental problem is associated with them.

obey

Law of conservation ? .........................................

in which the

Law of ? .........................................

Molecules or ? .................................

Chemical formulas

of

which give us information about the

6 Is collision theory compatible with the law of conservation of mass? Both of them explain certain aspects of the chemical reactions, but do they make use of the same scale? Explain your answers.

of

Reagents

Collide

7 The following table displays the masses of two substances while a chemical reaction takes place over time:

Number of Molecules or ? ................................

de

with enough

with proper

Energy

Orientation

and

which are expressed in the unit of amount of substance

? ...........................

Mole

122

of

Mass A/g

7,5

3,75

2,5

1,88

Mass B/g

1,7

3,4

6,8

13,6

Time/min

1

2

3

4

giving rise to

a) Are substances A and B, reagents or products of the reaction? Justify your answer.

Molecules or ? .................................

b) Graph the data of mass against time, and indicate if this is a linear relationship.

Solutions for all the numeric activities at anayaeducacion.es.

8

The image. Explain what this represents:

What similarities and differences are there between the previous representation and the following one?

Answer key Changes in composition 1 The change in the nature of matter refers to the change in its composition, or in other words, the substances that form this portion of matter being studied are altered.

9 How does temperature affect the rate of a chemical reaction? Use the collision theory and kineticmolecular theory on the temperature and the average kinetic energy of particles.

Representation of chemical reactions

Atomic theory of chemical reactions 5 Do all collisions that take place between the reagent particles cause them to break? Which factors does a collision depend on to be effective?

(2) Coefficients ? .................................

3 Indicate whether the following statements are true or false and explain why: a) Energy is released in all chemical reactions. b) Chemical reactions only occur naturally in living organisms. c) In a chemical reaction, reagents and products can be in different states of aggregation. d) Chemical reactions which take place in nature create an environmental problem.

4

c) From the previous chart, indicate in which time interval the rate of the chemical reaction is greatest. What do you base your answer on?

Connect this observation with the collision theory.

2 a) The reagents are vinegar and bicarbonate.

10 One student balances this chemical equation:

b) The products are sodium acetate and carbon dioxide.

NO + O2 8 NO2 as follows: NO + O2 8 NO3 Is what he has done right? Why?

11 Balance the following chemical reactions: c) NH3 + H2SO4 8 (NH4)2SO4 a) Al + O2 8 Al2O3 b) SO2 + O2 8 SO3 d) Fe2O3 + H2 8 Fe + H2O 12 Write all the information you can obtain from the following balanced chemical equation:

3 a) False; in some chemical reactions energy exchange takes place in the opposite direction.

3 Cl2 (g) + 2 Fe (s) 8 2 FeCl3 (s)

b) False; chemical reactions also occur in the inert natural environment, such as the precipitation of salts.

13 Use this table to verify that the reaction in the previous exercise is balanced.

Element

Atoms in reagents

Atoms in products

Cl Fe

123

c) False; many chemical reactions that take place in nature contribute to its balance.

4 Burning fossil fuels, such as methane (natural gas) or butane. They release carbon dioxide, which contributes to the anomalous greenhouse effect and, therefore, global warming and climate change.

Atomic theory of chemical reactions 5 Not all collisions are effective, it depends on the orientation and energy of the collision.

6 Both theories are compatible because they approach different aspects of the chemical reaction

and are not contradictory. The collision theory explains the chemical reactions from a microscopic point of view, where not all the collisions between reagent molecules give rise to products of the reaction, while the law of conservation of mass indicates that the sum of the masses of the reagents that have reacted is the same as the sum of the masses of the products formed, excluding in this balancing the amount of reagents that have not reacted, because the collisions have not been effective or the amount of one of them has been limited.

7 a) The substance A is a reagent of the reaction because there is less and less of it as time passes.

However, substance B is a product since its mass increases as time passes.

b) We show the variation of the masses of two substances over time on the same graph. The colour red is substance A and blue is substance B:

m/g 8 7 6 5 4 3 2 1 0

1

2

3

4

t /s

Neither of the two cases is a linear relationship. c) The mass variation is greater in the first time interval as the concentration of reagents at that time is greater, given that they have barely reacted. A greater concentration, a greater probability of collisions, and therefore, a greater reaction rate.

8 The first drawing shows a collision with the correct orientation in order to form the molecules of the products of the reaction, while the collision in the second picture does not have the correct orientation, and therefore, the chemical change does not take place.

9 When the temperature is increased, the molecules of the reagents move faster, and therefore, the

number of collisions with enough energy to result in the bonds breaking and forming new ones increases, giving rise to a greater production of product molecules per unit of time.

Representation of chemical reactions 10 It is not correct because they have changed the formula of the reaction product. The equation obtained does not have nitrogen dioxide as the product, but rather nitrogen trioxide.

11 a) 4 Al + 3 O2 8 2 Al2O3 b) 2 SO2 + O2 8 2 SO3

c) 2 NH3 + H2SO4 8 (NH4)2SO4 d) Fe2O3 + 3 H2 8 2 Fe + 3 H2O

12 Three moles of dichlorine, in gaseous state, react with two moles of iron in solid state to give two moles of iron(III) chloride.

13

70

Element Cl Fe

Atoms in reagents 3·2=6 2·1=2

Atoms in products 2·3=6 2·1=2

Unit

REVIEW 14 Write the balanced chemical equation from the information in this drawing, where red has been used for oxygen atoms, black for carbon atoms and white for hydrogen atoms.

19 When we heat up 50 g of calcium carbonate, 28 g of calcium oxide and carbon dioxide is formed.

16 Calculate the total number of atoms of each element in the reagents and in the products of the following chemical equations: a) 2 KOH + H2CO3 8 K2CO3 + 2 H2O b) 2 C2H6 + 7 O2 8 4 CO2 + 6 H2O c) 3 HCl + Al(OH)3 8 AlCl3 + 3 H2O

a) Zn (s) + Ag2O (s) 8 2 ZnO (s) + Ag (s)

d) H2S (g) + SO2 (g) 8 3 S (g) + H2O (g)

Fe

FeCl3

111.7

324.4

Mass/g

Water

54

Amount of substance/mol

3.16 · 1024 2.5

c) 1 mol of sulphuric acid.

Chemistry and environment 29

Look up information on the destruction of the ozone layer and the anomalous greenhouse effect.

Draw up a comparative table regarding these two environmental problems.

30

What makes you say that? In the combustion of hydrocarbons, one of the reaction products is carbon dioxide. The greater the number of carbon atoms in the hydrocarbon, the greater the amount of carbon dioxide that is produced.

24 Calculate how many atoms and molecules there are in the following samples: a) 18 g of water.

a) Calculate the mass of ammonia that can be obtained if 7.878 g of hydrogen react completely.

b) 88 g of carbon dioxide.

b) Using the law of conservation of mass, calculate the mass of nitrogen required in the reaction based on the previous data.

c) 81 g of aluminium.

anayaeducacion.es Check the ‘Let’s study’ and ‘Learn by playing’ sections in the resource bank.

124

a) What mass of iron has reacted? b) What mass of iron remains unreacted? Which percentage of the mass of the nail represents the part that has remained unreacted?

a) 0.25 mol of lead tetrachloride. b) 5 mol of water.

NH3 34.08

28 An iron nail of 5 g is left out in the open. After some time, we see a part has oxidised, forming 5 g of diiron trioxide:

23 Order the following amounts from the lowest to the highest according to mass:

Mass of products/g

N2

b) To verify the law of conservation of mass is obeyed, calculate the mass of HCl needed for 103.5 g of NaOH to react completely. What masses of sodium chloride and water are produced?

Total no. of O atoms

14 2 C2H2 + 5 O2 8 4 CO2 + 2 H2O 15 2 FeS2 (s) + 7/2 O2 (g) 8 2 SO2 (g) + Fe2O3 (s), o bien: 4 FeS2 (s) + 7 O2 (g) 8 4 SO2 (g) + 2 Fe2O3 (s) 16 a) Element Atoms in reagents Átomos en productos

mole of CO2/mole of fuel methane ethane

Data: m (K) = 39 u; m (H) = 1 u.

Amount of substance

Ozone

3 H2 + N2 8 2 NH3

28.02

c) If in the previous reaction, 20 g of potassium react with 9.21 g of water, what is the total amount of products obtained, in moles?

27 Hydrochloric acid (HCl) combines with sodium hydroxide (NaOH) to give sodium chloride (NaCl) and water: a) Write and balance the chemical equation.

Carbon dioxide

18 We have the following information about a chemical reaction:

H2

b) Calculate which mass of hydrogen gas is released in the previous reaction when 78 g of potassium react.

Mass of products/g

Cl2 212.7

Substance

I. ___CH ? ? 2 8 ___CO ? ? 2O 4 +___O 2 + ___H II. ___C ? 2H6 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H III. ___C ? 3H8 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H IV. ___C ? 4H10 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H b) One criterion to establish which one of the previous fuels is most polluting is to compare the amount of carbon dioxide released in the combustion of one mole of each one of them. Fill in the table with this information:

a) Write the balanced chemical equation.

22 Fill in the following table:

b) 2 NH4NO3 (s) 8 2 N2 (g) + H2O (g) + O2 (g) c) MgSO3 (s) 8 MgO (s) + SO2 (g)

Laws of chemical combination and chemical equations

6.06

+ ___CO ___SiO ? ? 8 ___Si ? ?

2 + ___C 2 b) Which carbon mass reacts with 1 kg of SiO2?

Data: M (Si) = 28,09 g/mol; M (O) = 16 g/mol; M (C) = 12 g/mol.

we use 531.75 g of chlorine and 300 g of iron. Are these amounts in stoichiometric ratio? Use the information from the table.

Mass of reagents/g

a) Balance the combustion reactions of methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10):

26 If we make potassium (K) react with water (H2O), potassium hydroxide (KOH) is formed and hydrogen gas (H2) is released.

3 Cl2 + 2 Fe 8 2 FeCl3

Calculate the mass of iron which will react and the mass of FeCl3 which forms.

17 Check that the following chemical reactions are well balanced. If they are not, correct them:

Mass of reagents/g

21 For the reaction of chlorine gas with iron:

4

For this reason, fuels with lower carbon numbers are preferably being used.

a) Balance the chemical reaction::

b) If we start from 150 g of reagent, which mass is obtained from each product?

20 From the previous exercise, obtain the proportion by mass at which calcium carbonate and calcium oxide react. Could we obtain 56 g of calcium oxide from 60 g of calcium carbonate? Which law have you based your answer to this activity on?

15 Iron disulphide, solid, combines with dioxygen and sulphur dioxide and diiron trioxide, solid, are obtained. Write the balanced chemical equation of this process, indicating the state of aggregation of all substances.

25 Silicon can be obtained from the reaction of SiO2 with coke (C) in an electric oven.

a) Which mass of carbon dioxide is formed?

propane butane

31

The objective of the combustion of hydrocarbons is to transform chemical energy into another kind of energy. In order to quantify the energy obtained in each reaction, we use the power of combustion parameter (PC), which is expressed in kilojoules (unit of energy) per mole of fuel (kJ/mol). The table shows the PC values of the fuels in the previous activity: Fuel CH4

PC/(kJ/mol) 890

C2H6

1 560

C3H8

2 220

C4H10

2 900

From these values, calculate, for each one, the amount of carbon dioxide released for each kilojoule of energy. Which fuel is most energyefficient? Which one releases less carbon dioxide into the atmosphere per kilojoule? Based on your results, what conclusions can you draw? Taking into consideration what you have learned, and goal 13.a, what fuel would you choose to produce energy?

What other sources of energy are in development to mitigate this fact? Check goal 7.2.

125

b)

ICT At anayaeducacion.es, students can look at the section ‘Let’s study!’ to reinforce and structure their knowledge about the content of the unit.

In addition, in the section ‘Learn by playing’, the students will find play activities which will allow them to self-assess their knowledge.

c)

K O

2·1=2 2·1+1·3=5

1·2=2 1· 3 + 2 · 1 = 5

H

2·1+1·2=4

2·2=4

C

1·1=1

1·1=1

Element

Atoms in reagents

Atoms in products

C

2·2=4

4· 1 = 4

H

2 · 6 = 12

6 · 2 = 12

O

7 · 2 =14

4 · 2 + 6 · 1 = 14

Element

Atoms in reagents

Atoms in products

H

3·1+1·3=6

3·2=6

Cl

3·1=3

1·3=3

Al

1·1=1

1·1=1

O

1·3=3

3·1=3

17 a) 2 Zn (s) + 2 Ag2O (s) 8 2 ZnO (s) + 4 Ag (s). The equation is not balanced. b) 2 NH4NO3 (s) 8 2 N2 (g) + 4 H2O (g) + 3 O2 (g). The equation is not balanced. c) MgSO3 (s) 8 MgO (s) + SO2 (g). The equation is balanced. d) 2 H2S (g) + SO2 (g) 8 3 S (g) + 2 H2O (g). The equation is not balanced.

Laws of chemical combination and chemical equations 18 a) Using the law of definite proportions, we get: mNH3 = 44.304 g de NH3. b) Now using the law of conservation of mass, we get: mN2 = 36.426 g de N2.

19 a) Based on the law of conservation of mass we have:

mCaCO3 = mCaO + mCO2 8 mCO2 = mCaCO3 – mCaO = 50 g – 28 g = 22 g Therefore, 22 g of carbon dioxide will be formed. b) Based on the law of definite proportions and the data of the activity, we have: 50 g 150 g mCaCO3 mCaO = 28 g = mlCaO We solve and find that the mass of calcium oxide is: m’CaO = 84 g. When we apply the law of conservation of mass again we have: mCO2 = mCaCO3 – mCaO = 150 g – 84 g = 66 g of carbon dioxide.

20 The proportion asked for is: 50 g mCaCO3 25 mCaO = 28 g = 14 = 1.7857 We apply the law of definite proportions and calculate the mass of CaCO3, which must be broken down to obtain 56 g of CaO: 50 g xg mCaCO3 mCaO = 28 g = 56 g We solve and find that x = 100 g of CaCO3. Therefore, it would not be possible to obtain 56 of CaO from 60 g of CaCO3, as 40 g of this reagent would be missing.

21 Taking into account the chemical reaction that takes place, and the stoichiometric masses that are needed and produced, we see that:

3 C l2 + 2 Fe 8 2 FeC l3

212,7 g 111,7 g

324.4 g

The ratio mFe/mC l2 is: 111.7 g mFe mC l2 = 212.7 g = 0.525 in the stoichiometric ratio 300 g mFe mC l2 = 531.75 g = 0.564 in the ratio proposed by the activity As they are the same, we will say that they are not in a stoichiometric ratio.

71

Unit

REVIEW 14 Write the balanced chemical equation from the information in this drawing, where red has been used for oxygen atoms, black for carbon atoms and white for hydrogen atoms.

19 When we heat up 50 g of calcium carbonate, 28 g of calcium oxide and carbon dioxide is formed.

16 Calculate the total number of atoms of each element in the reagents and in the products of the following chemical equations: a) 2 KOH + H2CO3 8 K2CO3 + 2 H2O b) 2 C2H6 + 7 O2 8 4 CO2 + 6 H2O c) 3 HCl + Al(OH)3 8 AlCl3 + 3 H2O

a) Zn (s) + Ag2O (s) 8 2 ZnO (s) + Ag (s) c) MgSO3 (s) 8 MgO (s) + SO2 (g) d) H2S (g) + SO2 (g) 8 3 S (g) + H2O (g)

Fe

FeCl3

111.7

324.4

Mass/g

a) Write and balance the chemical equation.

Water

54

Amount of substance/mol

Carbon dioxide

b) 5 mol of water.

Mass of products/g

N2

NH3 34.08

28 An iron nail of 5 g is left out in the open. After some time, we see a part has oxidised, forming 5 g of diiron trioxide:

2.5

a) What mass of iron has reacted? b) What mass of iron remains unreacted? Which percentage of the mass of the nail represents the part that has remained unreacted?

a) 0.25 mol of lead tetrachloride.

3 H2 + N2 8 2 NH3

28.02

b) To verify the law of conservation of mass is obeyed, calculate the mass of HCl needed for 103.5 g of NaOH to react completely. What masses of sodium chloride and water are produced?

Total no. of O atoms 3.16 · 1024

c) 1 mol of sulphuric acid.

Chemistry and environment 29

Look up information on the destruction of the ozone layer and the anomalous greenhouse effect.

Draw up a comparative table regarding these two environmental problems.

30

What makes you say that? In the combustion of hydrocarbons, one of the reaction products is carbon dioxide. The greater the number of carbon atoms in the hydrocarbon, the greater the amount of carbon dioxide that is produced.

24 Calculate how many atoms and molecules there are in the following samples: a) 18 g of water.

a) Calculate the mass of ammonia that can be obtained if 7.878 g of hydrogen react completely.

b) 88 g of carbon dioxide.

b) Using the law of conservation of mass, calculate the mass of nitrogen required in the reaction based on the previous data.

c) 81 g of aluminium.

anayaeducacion.es Check the ‘Let’s study’ and ‘Learn by playing’ sections in the resource bank.

mole of CO2/mole of fuel methane ethane

Data: m (K) = 39 u; m (H) = 1 u.

23 Order the following amounts from the lowest to the highest according to mass:

18 We have the following information about a chemical reaction:

H2

c) If in the previous reaction, 20 g of potassium react with 9.21 g of water, what is the total amount of products obtained, in moles?

27 Hydrochloric acid (HCl) combines with sodium hydroxide (NaOH) to give sodium chloride (NaCl) and water:

Amount of substance

Substance

IV. ___C ? 4H10 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H b) One criterion to establish which one of the previous fuels is most polluting is to compare the amount of carbon dioxide released in the combustion of one mole of each one of them. Fill in the table with this information:

b) Calculate which mass of hydrogen gas is released in the previous reaction when 78 g of potassium react.

Mass of products/g

Cl2 212.7

Ozone

Laws of chemical combination and chemical equations

124

Mass of reagents/g

111, 7 g mFe mFe mC l2 = 212.7 g = 531.75 g

I. ___CH ? ? 2 8 ___CO ? ? 2O 4 +___O 2 + ___H II. ___C ? 2H6 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H III. ___C ? 3H8 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H

a) Write the balanced chemical equation.

22 Fill in the following table:

b) 2 NH4NO3 (s) 8 2 N2 (g) + H2O (g) + O2 (g)

6.06

+ ___CO ___SiO ? ? 8 ___Si ? ?

2 + ___C 2 b) Which carbon mass reacts with 1 kg of SiO2?

Data: M (Si) = 28,09 g/mol; M (O) = 16 g/mol; M (C) = 12 g/mol.

we use 531.75 g of chlorine and 300 g of iron. Are these amounts in stoichiometric ratio? Use the information from the table.

The amount of iron that reacts will be:

a) Balance the combustion reactions of methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10):

26 If we make potassium (K) react with water (H2O), potassium hydroxide (KOH) is formed and hydrogen gas (H2) is released.

3 Cl2 + 2 Fe 8 2 FeCl3

Calculate the mass of iron which will react and the mass of FeCl3 which forms.

17 Check that the following chemical reactions are well balanced. If they are not, correct them:

Mass of reagents/g

21 For the reaction of chlorine gas with iron:

4

For this reason, fuels with lower carbon numbers are preferably being used.

a) Balance the chemical reaction::

b) If we start from 150 g of reagent, which mass is obtained from each product?

20 From the previous exercise, obtain the proportion by mass at which calcium carbonate and calcium oxide react. Could we obtain 56 g of calcium oxide from 60 g of calcium carbonate? Which law have you based your answer to this activity on?

15 Iron disulphide, solid, combines with dioxygen and sulphur dioxide and diiron trioxide, solid, are obtained. Write the balanced chemical equation of this process, indicating the state of aggregation of all substances.

25 Silicon can be obtained from the reaction of SiO2 with coke (C) in an electric oven.

a) Which mass of carbon dioxide is formed?

propane butane

31

The objective of the combustion of hydrocarbons is to transform chemical energy into another kind of energy. In order to quantify the energy obtained in each reaction, we use the power of combustion parameter (PC), which is expressed in kilojoules (unit of energy) per mole of fuel (kJ/mol). The table shows the PC values of the fuels in the previous activity: Fuel CH4 C2H6

PC/(kJ/mol) 890 1 560

C3H8

2 220

C4H10

2 900

From these values, calculate, for each one, the amount of carbon dioxide released for each kilojoule of energy. Which fuel is most energyefficient? Which one releases less carbon dioxide into the atmosphere per kilojoule? Based on your results, what conclusions can you draw? Taking into consideration what you have learned, and goal 13.a, what fuel would you choose to produce energy?

What other sources of energy are in development to mitigate this fact? Check goal 7.2.

125

8 mFe = 279.25 g of Fe

22 In order to calculate the amount of substance, the molar mass of each substance must be calculated

first based on the average atomic masses of the elements that form it and of the chemical formula.

So we have, for water, the molar of 18 g/mol; for the ozone, 48 g/mol, and for carbon dioxide, 44 g/ mol. Furthermore, in order to calculate the number of oxygen atoms in each substance, we need to know the Avogadro constant and the number of atoms of this element in each elementary entity (molecule in these cases), which is one for water, three for ozone and two for carbon dioxide.

Substance

mass/g

Amount of substance/mol

Number of total O atoms

Water

54

3

1.80 · 104

Ozone

83.96

1.75

3.16 · 104

Carbon dioxide

110

2.5

3.01 · 104

23 a) The mass of PbCl4 is: 0.25 m olde PbC l4 =

m M

8 m = nPbC l4 $ M = 0.25 m ol$ 348.99

b) The mass of H2O is: 5 m olde H 2O =

g

m M

8 m = nH 2O $ M = 5 m ol$ 18.02

m M

8 m = nH 2SO 4 $ M = 1 m ol$ 98.08

m ol

c) The mass of H2SO4 is: 1 m olde H 2SO 4 =

g m ol

= 87.25 g

= 90.1 g

g m ol

= 98.08 g

Therefore, mH 2SO 4 > mH 2O > mPbC l4 .

24 We calculate the molar mass, M, of the substance for all the cases, and using this value, we calculate

the amount of substance (in moles) by dividing the mass in grams by the molar mass. Lastly, we calculate the number of molecules by multiplying by the Avogadro constant and, using this value, the number of total atoms, taking into account how many atoms there are for each molecule in each case: n (mol) =

m (g) 8 N = n (mol) · NA (units/mol) g m Mc mol

The results are shown as a table: Formula

m/g

M/(g/mol)

n /mol

No. molecules No. of atoms

Water

H2O

18

18

1

6.022 · 10

1.8066 · 10

Carbon dioxide

CO2

88

44

2

1.2044 · 10

3.6132 · 10

Aluminium

Al

81

27

3

1.8066 · 10

1.8066 · 1024

25 The balanced chemical equation is: SiO2 + C 8 Si + CO2 We start with the mass data of SiO2, mSiO = 1 kg = 1000 g. In order to calculate the mass of carbon, 2 we must know the amount of SiO2, expressed in mol, in 1 kg of this substance. To do this, we calculate the molar mass of this compound: MSiO = 28.09 + 2 · 16 = 60.09 g/ mol 2

From the relationship between molar mass, mass and amount of substance, we get: m (g) n (mol) = 8 nSiO2 = 16, 64 mol g m Mc mol By observing the chemical equation we conclude that the amount of carbon needed, expressed in mol, will be the same as that which makes silicon oxide react; therefore: nCO = 16.64 mol 2

After applying the relationship between molar mass, mass and amount of substance again, we have: m (g) = M (g/mol) · n (mol) 8

mC = 12 g/mol · 16.64 mol = 199.7 g ≈ 200 g of carbon

26 a) 2 K + 2 H2O 8 2 KOH + H2 b) We start with the mass data of potassium, mK = 78 g. In order to calculate the mass of hydrogen, we must know the amount of K, expressed in mol, in 78 g of this substance. To do this, we start with the data of its molar mass, 39 g/mol: From the relationship between molar mass, mass and amount of substance, we get: m (g) n (mol) = 8 nK = 2 mol g m Mc mol

72

Unit

REVIEW 14 Write the balanced chemical equation from the information in this drawing, where red has been used for oxygen atoms, black for carbon atoms and white for hydrogen atoms.

19 When we heat up 50 g of calcium carbonate, 28 g of calcium oxide and carbon dioxide is formed.

16 Calculate the total number of atoms of each element in the reagents and in the products of the following chemical equations: a) 2 KOH + H2CO3 8 K2CO3 + 2 H2O b) 2 C2H6 + 7 O2 8 4 CO2 + 6 H2O

a) Zn (s) + Ag2O (s) 8 2 ZnO (s) + Ag (s) b) 2 NH4NO3 (s) 8 2 N2 (g) + H2O (g) + O2 (g) c) MgSO3 (s) 8 MgO (s) + SO2 (g) d) H2S (g) + SO2 (g) 8 3 S (g) + H2O (g)

FeCl3 324.4

Substance

Mass/g

Water

54

Amount of substance/mol

2.5

a) What mass of iron has reacted? b) What mass of iron remains unreacted? Which percentage of the mass of the nail represents the part that has remained unreacted?

a) 0.25 mol of lead tetrachloride. b) 5 mol of water.

NH3 34.08

28 An iron nail of 5 g is left out in the open. After some time, we see a part has oxidised, forming 5 g of diiron trioxide:

23 Order the following amounts from the lowest to the highest according to mass:

Mass of products/g

N2 28.02

b) To verify the law of conservation of mass is obeyed, calculate the mass of HCl needed for 103.5 g of NaOH to react completely. What masses of sodium chloride and water are produced?

Total no. of O atoms 3.16 · 1024

c) 1 mol of sulphuric acid.

Chemistry and environment 29

Look up information on the destruction of the ozone layer and the anomalous greenhouse effect.

Draw up a comparative table regarding these two environmental problems.

30

What makes you say that? In the combustion of hydrocarbons, one of the reaction products is carbon dioxide. The greater the number of carbon atoms in the hydrocarbon, the greater the amount of carbon dioxide that is produced.

24 Calculate how many atoms and molecules there are in the following samples: a) 18 g of water.

a) Calculate the mass of ammonia that can be obtained if 7.878 g of hydrogen react completely.

b) 88 g of carbon dioxide.

b) Using the law of conservation of mass, calculate the mass of nitrogen required in the reaction based on the previous data.

c) 81 g of aluminium.

anayaeducacion.es Check the ‘Let’s study’ and ‘Learn by playing’ sections in the resource bank.

mole of CO2/mole of fuel methane ethane

Data: m (K) = 39 u; m (H) = 1 u.

27 Hydrochloric acid (HCl) combines with sodium hydroxide (NaOH) to give sodium chloride (NaCl) and water:

Amount of substance

Ozone

3 H2 + N2 8 2 NH3

H2

c) If in the previous reaction, 20 g of potassium react with 9.21 g of water, what is the total amount of products obtained, in moles?

a) Write and balance the chemical equation.

Carbon dioxide

18 We have the following information about a chemical reaction:

124

Fe 111.7

nH = 1 mol

I. ___CH ? ? 2 8 ___CO ? ? 2O 4 +___O 2 + ___H II. ___C ? 2H6 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H

b) Calculate which mass of hydrogen gas is released in the previous reaction when 78 g of potassium react.

Mass of products/g

Cl2 212.7

By observing the chemical equation we conclude that the amount of hydrogen needed, expressed in mol, will be half of that which makes potassium react; therefore:

III. ___C ? 3H8 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H IV. ___C ? 4H10 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H b) One criterion to establish which one of the previous fuels is most polluting is to compare the amount of carbon dioxide released in the combustion of one mole of each one of them. Fill in the table with this information:

a) Write the balanced chemical equation.

22 Fill in the following table:

Laws of chemical combination and chemical equations

6.06

+ ___CO ___SiO ? ? 8 ___Si ? ?

2 + ___C 2 b) Which carbon mass reacts with 1 kg of SiO2?

Data: M (Si) = 28,09 g/mol; M (O) = 16 g/mol; M (C) = 12 g/mol.

we use 531.75 g of chlorine and 300 g of iron. Are these amounts in stoichiometric ratio? Use the information from the table.

Mass of reagents/g

a) Balance the combustion reactions of methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10):

26 If we make potassium (K) react with water (H2O), potassium hydroxide (KOH) is formed and hydrogen gas (H2) is released.

3 Cl2 + 2 Fe 8 2 FeCl3

Calculate the mass of iron which will react and the mass of FeCl3 which forms.

c) 3 HCl + Al(OH)3 8 AlCl3 + 3 H2O

17 Check that the following chemical reactions are well balanced. If they are not, correct them:

Mass of reagents/g

21 For the reaction of chlorine gas with iron:

4

For this reason, fuels with lower carbon numbers are preferably being used.

a) Balance the chemical reaction::

b) If we start from 150 g of reagent, which mass is obtained from each product?

20 From the previous exercise, obtain the proportion by mass at which calcium carbonate and calcium oxide react. Could we obtain 56 g of calcium oxide from 60 g of calcium carbonate? Which law have you based your answer to this activity on?

15 Iron disulphide, solid, combines with dioxygen and sulphur dioxide and diiron trioxide, solid, are obtained. Write the balanced chemical equation of this process, indicating the state of aggregation of all substances.

25 Silicon can be obtained from the reaction of SiO2 with coke (C) in an electric oven.

a) Which mass of carbon dioxide is formed?

propane

2

After applying the relationship between molar mass, mass and amount of substance again, we have:

butane

31

The objective of the combustion of hydrocarbons is to transform chemical energy into another kind of energy. In order to quantify the energy obtained in each reaction, we use the power of combustion parameter (PC), which is expressed in kilojoules (unit of energy) per mole of fuel (kJ/mol). The table shows the PC values of the fuels in the previous activity: Fuel CH4

PC/(kJ/mol) 890

C2H6

1 560

C3H8

2 220

C4H10

2 900

From these values, calculate, for each one, the amount of carbon dioxide released for each kilojoule of energy. Which fuel is most energyefficient? Which one releases less carbon dioxide into the atmosphere per kilojoule? Based on your results, what conclusions can you draw? Taking into consideration what you have learned, and goal 13.a, what fuel would you choose to produce energy?

What other sources of energy are in development to mitigate this fact? Check goal 7.2.

125

m (g) = M (g/mol) · n (mol) 8

mH = 2 g/mol · 1 mol = 2 g of H2 2

c) In this case, we start with the mass data of potassium, mK = 20 g. In order to calculate the mass of hydrogen, we must know the amount of K, expressed in mol, in 20 g of this substance. To do this, we start with the molar mass of this substance, 39 g/mol: From the relationship between molar mass, mass and amount of substance, we get: m (g) n (mol) = 8 nK = 0.513 mol g m Mc mol We then calculate the amount of hydrogen, for which we take into account the relationship between the stoichiometric coefficients of potassium and hydrogen and we conclude that the amount of hydrogen, expressed in mol, will be half of that which makes potassium react: nH = 0.256 mol 2

In order to calculate the amount of potassium hydroxide, we take into account that the stoichiometric coefficients of potassium and of potassium hydroxide are equal; therefore, the amount of these substances (expressed in mol) is the same: nKOH = 0.513 mol The total amount obtained will be: n = 0.256 mol + 0.513 mol = 0.769 mol

27 a) The chemical equation is: HCl + NaOH 8 NaCl + H2O b) Knowing that 103.5 g of NaOH react completely, we calculate the amount of substance it is equal to: 103, 5 g m n= = = 2, 59 m ol M 40 g/m ol By stoichiometry, we see that the same amount of substance of NaOH reacts as the amount of the other components of the reaction. Therefore, the masses of the other compounds will be: g mH C l = n $ M = 2.59 m ol$ 36.46 = 94.34 g m ol g mH 2O = n $ M = 2.59 m ol$ 18.02 = 46.63 g m ol g mN aC l = n $ M = 2.59 m ol$ 58.44 = 151.21 g m ol In order to check if the law of conservation of mass is fulfilled, we have to prove that the sum of the masses of the reagents is equal to the sum of the masses of the products: mN aO H + mH C l = mN aC l + mH 2O 103.5 g + 94.34 g = 46.63 g + 151.21 g 197.84 g = 197.84 g 8

yes,it is fulfilled

28 The chemical reaction that takes place is: 4 Fe + 3 O2 8 2 Fe2O3 a) In order to know the amount of iron that reacts, we start with the 5 g of Fe2O3 that we obtain.

Firstly, we calculate the amount of substance equal to: 5g m n= = = 0.031 m olof Fe2O 3 M 159.7 g/m ol By reaction stoichiometry, we calculate the amount of substance of iron that reacts: 4 m olof Fe x = 2 m olof Fe2O 3 0.031 m olof Fe2O 3

8

x = 0.062 m olof Fe

From this data, we calculate the mass which is equal to: g m = n $ M = 0.062 m ol$ 55.85 = 3.5 g ofFe m ol b) The mass of iron which remains unreacted is: mFe (remaining) = mtotal – mreaction = 5 g – 3.5 g = 1.5 g The percentage that this represents is: % Fe unreacted =

1.5 g 5.0 g

$ 100 = 30 %

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Unit

REVIEW 14 Write the balanced chemical equation from the information in this drawing, where red has been used for oxygen atoms, black for carbon atoms and white for hydrogen atoms.

19 When we heat up 50 g of calcium carbonate, 28 g of calcium oxide and carbon dioxide is formed.

16 Calculate the total number of atoms of each element in the reagents and in the products of the following chemical equations: a) 2 KOH + H2CO3 8 K2CO3 + 2 H2O b) 2 C2H6 + 7 O2 8 4 CO2 + 6 H2O c) 3 HCl + Al(OH)3 8 AlCl3 + 3 H2O

a) Zn (s) + Ag2O (s) 8 2 ZnO (s) + Ag (s)

d) H2S (g) + SO2 (g) 8 3 S (g) + H2O (g)

Fe

FeCl3

111.7

324.4

Mass/g 54

Carbon dioxide

3.16 · 1024 2.5

b) 5 mol of water.

Mass of products/g

N2

NH3 34.08

a) What mass of iron has reacted? b) What mass of iron remains unreacted? Which percentage of the mass of the nail represents the part that has remained unreacted?

c) 1 mol of sulphuric acid.

Chemistry and environment 29

Look up information on the destruction of the ozone layer and the anomalous greenhouse effect.

Draw up a comparative table regarding these two environmental problems.

30

What makes you say that? In the combustion of hydrocarbons, one of the reaction products is carbon dioxide. The greater the number of carbon atoms in the hydrocarbon, the greater the amount of carbon dioxide that is produced.

24 Calculate how many atoms and molecules there are in the following samples: a) 18 g of water.

a) Calculate the mass of ammonia that can be obtained if 7.878 g of hydrogen react completely.

b) 88 g of carbon dioxide.

b) Using the law of conservation of mass, calculate the mass of nitrogen required in the reaction based on the previous data.

c) 81 g of aluminium.

anayaeducacion.es Check the ‘Let’s study’ and ‘Learn by playing’ sections in the resource bank.

124

28 An iron nail of 5 g is left out in the open. After some time, we see a part has oxidised, forming 5 g of diiron trioxide:

a) 0.25 mol of lead tetrachloride.

3 H2 + N2 8 2 NH3

28.02

b) To verify the law of conservation of mass is obeyed, calculate the mass of HCl needed for 103.5 g of NaOH to react completely. What masses of sodium chloride and water are produced?

Total no. of O atoms

23 Order the following amounts from the lowest to the highest according to mass:

18 We have the following information about a chemical reaction:

mole of CO2/mole of fuel methane ethane

Data: m (K) = 39 u; m (H) = 1 u.

27 Hydrochloric acid (HCl) combines with sodium hydroxide (NaOH) to give sodium chloride (NaCl) and water: a) Write and balance the chemical equation.

Amount of substance/mol

Ozone

Laws of chemical combination and chemical equations

H2

c) If in the previous reaction, 20 g of potassium react with 9.21 g of water, what is the total amount of products obtained, in moles?

Amount of substance

Water

IV. ___C ? 4H10 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H b) One criterion to establish which one of the previous fuels is most polluting is to compare the amount of carbon dioxide released in the combustion of one mole of each one of them. Fill in the table with this information:

b) Calculate which mass of hydrogen gas is released in the previous reaction when 78 g of potassium react.

Mass of products/g

Cl2 212.7

Substance

I. ___CH ? ? 2 8 ___CO ? ? 2O 4 +___O 2 + ___H II. ___C ? 2H6 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H III. ___C ? 3H8 + ___O ? 2 8 ___CO ? ? 2O 2 + ___H

a) Write the balanced chemical equation.

22 Fill in the following table:

b) 2 NH4NO3 (s) 8 2 N2 (g) + H2O (g) + O2 (g) c) MgSO3 (s) 8 MgO (s) + SO2 (g)

6.06

+ ___CO ___SiO ? ? 8 ___Si ? ?

2 + ___C 2 b) Which carbon mass reacts with 1 kg of SiO2?

Data: M (Si) = 28,09 g/mol; M (O) = 16 g/mol; M (C) = 12 g/mol.

3 Cl2 + 2 Fe 8 2 FeCl3

Mass of reagents/g

a) Balance the combustion reactions of methane (CH4), ethane (C2H6), propane (C3H8) and butane (C4H10):

26 If we make potassium (K) react with water (H2O), potassium hydroxide (KOH) is formed and hydrogen gas (H2) is released.

we use 531.75 g of chlorine and 300 g of iron. Are these amounts in stoichiometric ratio? Use the information from the table.

Calculate the mass of iron which will react and the mass of FeCl3 which forms.

17 Check that the following chemical reactions are well balanced. If they are not, correct them:

Mass of reagents/g

21 For the reaction of chlorine gas with iron:

4

For this reason, fuels with lower carbon numbers are preferably being used.

a) Balance the chemical reaction::

b) If we start from 150 g of reagent, which mass is obtained from each product?

20 From the previous exercise, obtain the proportion by mass at which calcium carbonate and calcium oxide react. Could we obtain 56 g of calcium oxide from 60 g of calcium carbonate? Which law have you based your answer to this activity on?

15 Iron disulphide, solid, combines with dioxygen and sulphur dioxide and diiron trioxide, solid, are obtained. Write the balanced chemical equation of this process, indicating the state of aggregation of all substances.

25 Silicon can be obtained from the reaction of SiO2 with coke (C) in an electric oven.

a) Which mass of carbon dioxide is formed?

propane butane

31

The objective of the combustion of hydrocarbons is to transform chemical energy into another kind of energy. In order to quantify the energy obtained in each reaction, we use the power of combustion parameter (PC), which is expressed in kilojoules (unit of energy) per mole of fuel (kJ/mol). The table shows the PC values of the fuels in the previous activity: Fuel CH4

PC/(kJ/mol)

29 In this activity, students will compare the similarities and differences, taking into account that both are global environmental problems, not local ones, which are gradual, caused by factors derived from industrial progress and which affect the composition of the atmosphere due to the accumulation of gases in unnatural concentrations. There are several differences between them, especially: direct effects on health, medium-term solutions, effects on climate, different causes.

30 a) The balanced chemical equations are: I. CH4 + 2 O2 8 CO2 + 2 H2O

890

C2H6

1 560

C3H8

2 220

C4H10

2 900

From these values, calculate, for each one, the amount of carbon dioxide released for each kilojoule of energy. Which fuel is most energyefficient? Which one releases less carbon dioxide into the atmosphere per kilojoule? Based on your results, what conclusions can you draw? Taking into consideration what you have learned, and goal 13.a, what fuel would you choose to produce energy?

What other sources of energy are in development to mitigate this fact? Check goal 7.2.

125

ICT To work on searching for information, activity 29 asks students to critically select information, using a search engine, about two environmental problems in order to prepare a table.

II. C2H6 +

7 O 8 2 CO2 + 3 H2O 2 2

III. C3H8 + 5 O2 8 3 CO2 + 4 H2O IV. C4H10 +

13 O2 8 4 CO2 + 5 H2O 2

b) Looking at the above equations, we have: nCO2/nfuel

Developing thinking At anayaeducacion.es there is an explanatory document of the technique ‘What makes you say that?’, which we suggest for developing the answer to activity 30.

SDG commitment At anayaeducacion.es there are videos relating to goals 13.a and 7.2. Watching them will help students draw the conclusions that are sought by the questions in activity 31.

methane

1

ethane

2

propane

3

butane

4

31 In order to calculate the amount of CO2 per each kilojoule of energy obtained in the combustion of the above hydrocarbons, we have to divide the number of moles of carbon dioxide emitted per each mole of fuel by the calorific power of each of them. The results are shown in the table: nCO2/nfuel

PC/(kJ/mol)

nCO2/kJ

methane

1

890

0.001124

ethane

2

1 560

0.001282

propane

3

2 220

0.001351

butane

4

2 900

0.001379

It can be seen that the fuel that generates the lowest amount of carbon dioxide per each unit of transformed energy is methane; therefore, it is the least polluting. However, the difference between them is not significant.

74

notes

75