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qwertyuiopasdfghjklzxcvbnmqwertyui opasdfghjklzxcvbnmqwertyuiopasdfgh jklzxcvbnmqwertyuiopasdfghjklzxcvbn mqwertyuiopasdfghjklzxcvbnmqwerty CHEMICAL REACTIONS Part one. A qualitative aproach to chemical uiopasdfghjklzxcvbnmqwertyuiopasdf reactions ghjklzxcvbnmqwertyuiopasdfghjklzxcv bnmqwertyuiopasdfghjklzxcvbnmqwe rtyuiopasdfghjklzxcvbnmqwertyuiopas dfghjklzxcvbnmqwertyuiopasdfghjklzx cvbnmqwertyuiopasdfghjklzxcvbnmq wertyuiopasdfghjklzxcvbnmqwertyuio pasdfghjklzxcvbnmqwertyuiopasdfghjk lzxcvbnmqwertyuiopasdfghjklzxcvbnm qwertyuiopasdfghjklzxcvbnmrtyuiopas dfghjklzxcvbnmqwertyuiopasdfghjklzx cvbnmqwertyuiopasdfghjklzxcvbnmq wertyuiopasdfghjklzxcvbnmqwertyuio pasdfghjklzxcvbnmqwertyuiopasdfghjk lzxcvbnmqwertyuiopasdfghjklzxcvbnm qwertyuiopasdfghjklzxcvbnmqwertyui 19/04/2013

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chemical reactions

Exercise 0; Work in pairs. Speak with your partner about thsese questions; what do you know about chemical processes? Do you think it is going to be useful or useless what you will learn? Antonio Becerra Hernรกndez. I.E.S. Manuel de Falla.

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1. DIFFERENT PROCESSES IN NATURE

Look around you. It is easy to realise that phenomenas are always happening in Nature. In general, we can classify these changes in two types, physical processes and chemical processes. Matter undergoes chemical change when the composition of the substances changes. In other words, one or more substances combine or break up to form new substances. When a process in an object does not change its chemical nature, we call it physical change

Exercise 1: Give 3 examples of chemical changes and 3 of physical changes.

Exercise 2: Work in pairs. Look at these images and match them with chemical change or physical change.

How can we know that a chemical change has happened? If pure substances are going to be converted into different pure substances the characteristic properties of matter must change because they depend on chemical composition. That means that color changes, bubbles formation, heat involved, etc, are different ways to show us a chemical reaction is happening.

Exercise 3: You went to the lab with your teacher to see what happens when you place a little piece of sodium into water, just as you can see it in this image. Write your observations down and decide if it was a chemical reaction what you saw.

Antonio Becerra Hernรกndez. I.E.S. Manuel de Falla.

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Exercise 4: Your teacher is giong to show you what happens when you mix different susbtances. You have to write down what you see and try to decide if that maens a chemical reaction was carried out.

Exercise 5: Word in pairs. Choose a process which you think it is a chemical one and another which is not. Give your partner reasons for those choices using these kind of expressions... As long as matter is going to suffer changes ... I guess that is a chemical process/physical process because... You can realise that changes in … If you watch carefully …

Exercise 6: Listening. You are going to hear different processes and you have to fill in this table with them. Do it in your notebook. Click here to listen Chemical processes

Physical processes

2. CHEMICAL ECUATIONS We have to look for a way to represent chemical changes which has to be easy to deal with. To do that, you have to make a chemical formula of each susbtance involved in the process, writing first substances which are going to disapear (reactants) and then substances which are going to be created (products). Sometimes you have to indicate the aggregate state of each substance in brakets.

REACTANTS → PRODUCTS For example, if you mix hygrogen and oxygen in a closed container and you produce a spark inside, water is going to be produced. A chemical change happens and this is its chemical ecuation:

hygrogen + oxygen → water and even better, using formulas

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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H2 + O2 → H2O Is it possible to improve this chemical ecuation? Yes, it is and you are going to know how to do it. But we have to find out what a quemical reaction is under a microscopic point of view.

Exercise 7: Look at this image and try to describe what it is representing using the following words or expressions: atoms of hydrogen... atoms of oxygen … ...are going to break free... molecules of water... ...are going to join... ...be formed...

Now, we are ready to define what a chemical reaction is, and to write down our chemical equation in the best way. “A chemical reaction is a process that leads to the transformation of one set of chemical substances to another, involving the forming and the breaking of chemical bonds between atoms, with not change to the nuclei (therefore no change to the elements present). That means in chermical processes substances are going to change but the atoms involved are going to be the same, in quality and in quantity.” For example, the following equation doesn’t make sense at all. Na + H2O → KOH + H2 Exercise 8: What is the reason this equation is wrong? We are going to consider the formation of water again. If in a chemical process does not change atoms, it is only going to change bonds between them, we have to write the equation down making sure that the same number of each kind of atom are in both sides of the equation ( reactants and products ). To do that, we used whole numbers placed before the formula of the substances. In our example; 2 H2 + O2 → 2 H2O

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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And this is the best way to write the chemical equation down. We call it balanced chemical equation. Exercise 9: Look at the following picture and write down the right balanced chemical ecuation if you think that the whole numbers are correct.

Exercise 10: Work in pairs. Read carefully the next phrase which is going to be very important in the next exercise. “Keep in mind that you can not change the compounds and elements that are reacting. This means all of the subscripts must remain unchanged”. Discuss with your partner this important rule to balence chemical reactions and link it to what a chemical reaction is really.

Exercise 11: Work in pairs. Try to balance the following chemical equations. If you find equations which don’t make sense, indicate it. a) b) c) d) e) f)

H2 + Fe2O3 → H2O + Fe C3H6 + O2 → CO2 + H2O KClO3 → KCl + O2 Fe + O2 → Ni2O3 FeS2 + O2 → SO2 + Fe2O3 HCl + Al(OH)3 → AlCl3 + H2O

Are you ready for our next step to undertand what a chemical reaction is? I hope so, because we need now to know how a chemical process is started by a microscopic point of view. As always in science, we have to look for a theory which matches experimental data.

Exercise 12; Read the next text and answer the questions. Collision theory says that a chemical reaction can only occur between particles when they collide (hit each other). Particles may be atoms, ions or molecules. Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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There is a minimum amount of energy which colliding particles need in order to react with each other. If the colliding particles have less than this minimum energy then they just bounce off each other and no reaction occurs. This minimum energy is called the activation energy. The faster the particles are going, the more energy they have. Fast moving particles are more likely to react when they collide. You can make particles move more quickly by heating them up (raising the energy). 1.Collision theory says that a chemical reaction can only take place when particles … a) collide b) turn very hot c) get on well with each other 2. An increase in temperature... a) will turn particles positive b) will incresase the rate of reaction c) will decrease the rate of reaction 3. The minimum amount of energy needed for colliding particles to react is called … a) the rest energy b) the funny energy c) the activation energy

Exercise 13: Work in pairs. Each member of the group has to fill in only one column in the following table. Afterward she/he must give reasons to her/his partner about their conclusions.

Microscopic point of view...what is needed for Macroscopic point of view...what we are going a chemical reaction to happen to see when a chemical reaction happens

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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3. LAVOISIER'S LAW OF CONSERVATION OF MASS The Law of Conservation of Mass (or Matter) in a chemical reaction can be stated in the following way: In a chemical reaction, matter is neither created nor destroyed. It was discovered by Antoine Laurent Lavoisier (1743-94) about 1785. However, philosophical speculation and even some quantitative experimentation preceeded him. In addition, he was certainly not the first to accept this law as true or to teach it, but he is credited as its discoverer.

Exercise 14: For many people Lavoisier can be considerer the firstgreat quemist in history. Find out something about his life and about what he did to boost our scientific knowledge.

Exercise 15: Work in pairs. Consider the following chemical reaction. 2 H2 + O2 → 2 H2O a) If we mix in a closed container 4 grams of hydrogen with 32 grams of oxygen and produce a spark, 36 grams of water are going to be formed. One member of the group has to “read” the equation in term of molecules and another in term of grams. Discuss if both ways of reading are coherent with each other. b) What do you think is going to happen if we mix 5 grams of hydrogen with 32 grams of oxygen? c) Find out what Proust law of definete composition says and try to relate it to the last question. Exercise 16 : In the reaction shown below, 2Al) + 3BaO → Al2O3 + 3Ba 65.0 g of Aluminum reacted with 35.0 g of Barium oxide to produce aluminum oxide and barium. If 84.0 g of aluminum oxide is produced, how much barium is produced? Exercise 17: You have a chemical in a sealed glass container filled with air. The system has a mass of 250.0 g. The chemical is ignited by means of a magnifying glass focusing sunlight on the reactant. After the chemical is completely burned, what is the mass of the system?

4. SPEED OF REACTION. The reaction rate (rate of reaction) or speed of reaction for a reactant or product in a particular reaction is intuitively defined as how fast or slow a reaction takes place. For example, the oxidative rusting of iron under the atmosphere is a slow reaction that can take many years, but the combustion of cellulose in a fire is a reaction that takes place in fractions of a second. Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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Let’s watch this video. It is not esay to follow it up but you can try your best and use subtitles if you want. In any case try to get the main ideas at least. How to speed up chemical reactions

Exercise 18: Write down five ways to increase the speed of a chemical reaction.

5. ENERGY CHANGES IN CHEMICAL REACTIONS All chemical reactions involve energy changes. When a chemical reaction occurs, bonds in the reactants break, while new bonds form in the products. In some reactions, the energy that must be absorbed to break the bonds in the reactants, is less than the total energy that is released when new bonds are formed. This means that in the overall reaction, energy is released as either heat or light. This type of reaction is called an exothermic reaction. Another way of describing an exothermic reaction is that it is one in which the energy of the products is less than the energy of the reactants, because energy has been released during the reaction. We can represent this using the following general formula: Reactants→Product+Energy

In other reactions,the energy that must be absorbed to break the bonds in the reactants, is more than the total energy that is released when new bonds are formed. This means that in the overall reaction, energy must be absorbed from the surroundings. This type of reaction is known as an endothermic reaction. Another way of describing an endothermic reaction is that it is one in which the energy of the products is greater than the energy of the reactants, because energy has been absorbed during the reaction. This can be represented by the following formula: Reactants+Energy→Product

Exercise 19 : Read the next text and answer the questions.

Chemical reactions involve breaking bonds in reactants and forming new bonds in products. Breaking bonds requires energy, and forming bonds releases energy. The energy associated with bonds is called bond energy. What happens to this energy during a chemical reaction? Chemists have determined the bond energy for bonds between atoms. Breaking a bond between carbon and hydrogen requires a certain amount of energy. This amount of energy is different from the amount of energy needed to break a bond between carbon and oxygen, or between hydrogen and oxygen. Energy is needed to break bonds in reactant molecules. Energy is released when bonds are formed in product molecules.By adding up the bond energies in the reactants and products, you Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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can determine whether energy will be released or absorbed. If more energy is released when the products form than is needed to break the bonds in the reactants, then energy is released during the reaction. A reaction in which energy is released is called an exothermic reaction

If more energy is required to break the bonds in the reactants than is released when the products form, then energy must be added to the reaction. That is, the reaction absorbs energy. A reaction in which energy is absorbed is called an endothermic reaction. These types of energy changes can also be observed in different physical changes such as dissolving or changing state. The state change from a liquid to a solid, or freezing, releases energy—this is an exothermic process. The state change from a solid to a liquid, or melting, absorbs energy—this is an endothermic process. Questions: 1. In which ways might an exothermic reaction release energy? 2. Fill in the gaps

Jellyfish glows because of __________ Chemical reactions.

The bombardier beetle, shown in the photograph below this text, uses natural exothermic ________to defend itself. Although several chemical reactions are involved, the end result is the production of a hot, toxic spray.The most important reaction in the process is the decomposition of hydrogen peroxide into _____and _________. 2 H2O2 → 2 H2O + O2 When the hydrogen peroxide rapidly breaks down, the hot, toxic mixture made by the series of reactions is pressurized by the ________ gas from the reaction in the equation above. After enough pressure builds up, the beetle can spray the mixture.

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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6. CHEMICAL REACTIONS OF INTEREST. COMBUSTION REACTIONS. Combustion is a chemical reaction chemical that occurs between a fuel and an oxidizing agent that produces energy, usually in the form of heat and light. An example might be the combustion of methanol and this is its equation. CH3OH + O2 → CO2 + H2O Exercise20 : Balance this equation. Exercise 21: Identify which of these processes are combustions and balance them. a) CH4 + O2 → CO2 + H2O b) HCl + NaOH → NaCl + H2O c) C4H10 + O2 → CO2 + H2O Exercise 22: Why do you think this kind of chemical reaction is so important for human beings?

Exercise 23 : Find out how a bunsen burner works. To do that you have to go to the lab and listen to your teacher. Write down the equation of the chemical process related to this burner. Exercise 24: Work in group. Each group is going to get a alcohol burner. You have to do the same that in the last exercise by yourself. What is the reason the burner is going to set off if the cap is put in place?

7. CHEMICAL REACTIONS OF INTEREST. ACID-BASE REACTIONS Substances have long been classified as acids or bases according to some general properties which are summarized below. Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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Acids properties

Bases properties

When dissolved in water, acids: -

When dissolved in water, bases:

Conduct electricity Have a sour taste React with bases to neutralize their properties React with active metals to liberate hydrogen.

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Conduct electricity Have a slippery feeling React with acids to neutralize their properties.

This year you don´t have to learn the concept of acid or base. The only thing that you have to learn is how to identify some of them by their formula and there we go... The most common acids have hydrogen in their formulas: examples; HCl, H2SO4, H2S, HNO3. Some bases have the group OH in their formulas: examples; NaOH, KOH, Ca(OH)2. Therefore, we can say that acid substances are going to deliver hygrogen ions into solution ( H+ ) and bases are going to deliver hydroxides ions ( OH- ) into solution. Acid-bases reactions: When an acid and a base are placed together, they react to neutralize the acid and base properties, producing a salt. For example HCl + NaOH → NaCl + H2O Acid + base → salt + water Acidity depends on how many hydrogen ions are in solution and we have a scale to measure it which is called pH scale. The higer the concentration of hydrogen ions is in solution, the lower the value of pH is. This scale goes from 0 to 14 and we don´t use units.

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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Exercise 25: This exercise is a review of the entire unit. You have to do it on your computer. This exercise was made using “hot potatoes”. exercises

Exercise 26: Work in little groups.Take a look at this picture which tries to sum up the unit and share what you learn with your partner.

Groups are going to be formed. Each group has to have three or four students and it is going to be eight groups in total. Each group has to develop one proyect and these are the remarks that you have to consider when you deal with your proyect -

You are going to get a piece of information about what you have to do in the lab but you are giong to be the ones who develop the proyect and you have to get the final product by your own. However, you will have your teacher’s help if you ask for it.

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You have to prepare a little experience in the lab about your proyect and you have to give a speech about your theme using a presentation. Each member of the group has to participate in the speech. You are going to have a maximum of 15 minutos for all this.

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You have to use the knowledge you got in this unit, but you have to do a little invesigation finding out what you nee, using the internet, science books, your teachers’ help, etc.

You can see below the list of proyects. Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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1. Electroquemistry. Chemical reaction between copper and aluminium in a acid medium. Chemical reaction between copper and zinc...how can you get profit of this?. The daniel Cell. 2. Speed of reaction. Factors that affect the chemical reaction rate (I). Peroxide hydrogen decomposition. Influence of contact surface between reactants, concentration and temperature. 3. Speed of reaction. Factor that affect the chemical reaction rate (II). Peroxide hydrogen decomposition. Influence of catalysts. Influence of light in silver reduction. 4. Energy changes in processes. Ammonia chloride and water. Sodium hydroxide and water. Find out endothermic and exothermic chemical processes and show us in the lab. 5. Acid-base indicators. What are they?. Get an indicator from a lombard and show us how it behaves in different medium depending on pH Scale value. Do the same with other indicators. 6. Tha blue magic bottle. You will have to perform what happens when you play with glucose and methylene blue in alkaline media (NaOH). 7. Chemical volcanoes. Build up a volcanoe taking advantaging of acid-base chemical reactions. Try to perform another volcanoe considering decomposition of ammonium dichromate now. 8. Electrolisys of potassium iodide (KI). Try to find out interesting ways of showing this beautiful chemical reaction using different devices.

Exercise 27; What have you learned? Self-assessment.

Skills involved

I can... Yes, I can

I am not sure I can

I am afraid, I can’t

Understand if I hear about what is the difference

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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between a chemical process and a physical process Understand texts about chemical reactions

Explain what a chemical process is Give examples of chemical processes

Write down the equation of a chemical process Balance a chemical equation

Speak about the most important chemical reactions as combustions and acib-bese reactions Write down the difference between an endothermic and an exothermic process Look for information about chemical reactions on the internet and books Speak about a specific chemical process if I work on it at home Understand other people if they speak about chemical reactions in a easy way Solve out quantitative questions about Lavoisier’s law

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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Exercise 28: Let’s consider your oppinion. Fill in the following questionnaire.Click here

Antonio Becerra Hernández. I.E.S. Manuel de Falla.

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