St. George's College
Subject: 8th CHEMISTRY
Class: Types of
Chemical Reactions
Date: October 19th
Teacher's notes
Objectives
Vocabulary Link and Learn
In‐Class Survey
Prepared by
2009 1
8th Milton A ‐ Chemistry of Water Name
Oral Intervention
Blackmark
Sergio María Fernanda Alejandra Almendra Anna Paula Sandra E‐C Maia María Belén Alfredo Kinley Arianne Sandra M. Fiorella Cristina Giulia Jaime Stefano Bruno
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8th Milton Alpha ‐ Chemistry of Water Name
Oral Intervention
Blackmark
Marcelo Antonella Paulo Alejandro Brenda Diego Gabriel Valeria Giuliana Joshua María Gracia Gonzalo N. Rodrigo Paolo Gonzalo R. Giorgio Nicolás María Claudia
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Let's remember previous learned concepts...
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What are Chemical Reactions?
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New knowledge beginning......
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Collision Theory • The Collision Theory is the current model that explains how a chemical reaction happens. It was proposed by Lewis and others in the 1920s. • For a chemical reaction to happen, it is necessary for the atoms, molecules or ions to come in contact with each other. • This contact happens through collisions. • When matter react, not all the mass contained in a substance reacts and is transformed completely into product (s), because not all collisions cause the chemical bonds to be broken.
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http://bit.ly/34RHyG
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Collision Theory • For a chemical reaction to take place, two things must happen : 1. That the atoms, molecules or ions of the reactants must have enough energy (kinetic), for collisions to be able to break chemical bonds and form new ones. 2. That the collision takes place under an adequate orientation, because the reactants may have enough energy for the collision to happen, but the reaction will not take place if the orientation is not efficient.
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Energy of Activation • According to the first condition, the minimum energy required for a reaction to happen is called Activation Energy. • The Activation Energy is referred to as the energetic barrier to climb for a chemical reaction to happen.
http://bit.ly/Iopos
http://bit.ly/1cIor2
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http://bit.ly/Iopos
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Types of Chemical Reactions Chemical reactions in Inorganic Chemistry are usually classified based on the possible reactions from the substances called reactants: • Synthesis Reactions • Decomposition Reactions • Combustion Reactions • Single‐Replacement Reactions • Double‐Replacement Reactions
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Synthesis or Addition Reactions • Are the reactions where two or more substances react to form ONE new substance. • This is a general representation of a synthesis reaction:
A + B → C where reactant A is combined with reactant B to produce the new substance C.
2 H2 + O2 → 2 H2O CaO + H2O → Ca(OH)2 S + Fe → FeS
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Decomposition or Analysis Reactions • When one substance chemically reacts to form two or more new substances. • There are two types of decomposition reactions: 1. Simple Decomposition Is a type of chemical reaction that is the opposite of the synthesis reaction. One substance is decomposed in two or more products. This is a general representation:
A → B + C where substance A generates products B and C.
2. Decomposition through a Reactant In this case, another reactant is necessary. It can be represented as:
AB + C → AC + BC where substance AB reacts in the presence of substance C to be transformed into tow different substances, AC and BC. 16
Combustion Reactions • An element or a compound reacts with oxygen, producing energy in the form of heat and light.
H2(g) + O2(g) H2O(g) • This looks like a synthesis reaction! • When the reactant is a hydrocarbon (contains H and C), the product will be carbon dioxide gas, water vapor, and energy. • Propane gas (C3H8) in a grill reacts with oxygen gas to yield carbon dioxide gas, water vapor and heat energy.
C3H8(g) + O2(g) CO2(g) + H2O(g) + energy
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Single‐Replacement Reactions • In this case, a substance replaces one of its places with another substance, so the replaced element is released:nente sustituido queda libre.
A + BC → AC + B • In this type of reaction, the most reactive substances taje the place of the less reactive substances. CuSO4 + Zn → ZnSO4 + Cu 2 HCl + Mg → MgCl2 + H2 HgS + Fe → Hg + FeS
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Double‐Replacement Reactions • It is said that when two substances react and exchange their ions (anion and cation), a double‐displacement reaction has taken place.
AB + CD → AD + CB 2 NaOH + H2SO4 → Na2SO4 + 2 H2O BaCl2 + 2 AgNO3 → 2 AgCl + Ba(NO3)2 (NH4)2S + HgBr2 → 2 NH4Br + HgS
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Identify the following reactions +
NaOH + Al(NO3)3 NaNO3 + Al(OH)3
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YouTube Video Five Major Chemical Reactions http://www.youtube.com/watch?v=tE4668aarck
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Acid‐Base Reactions • The reaction from an acid and a base is called Neutralization Reaction, and is a reaction where a transfer of protons occurs.
2 HCl + Ca(OH)2 → CaCl2 + 2 H2O • In the Neutralization reactions between an acid and a base, two substances are formed: a Salt and Water.
Base Gains PROTON
Acid Loses PROTON
Conjugated Acid from H2O
Conjugated Base from HCl 22
REDOX Reactions • Oxidati0on was initially defined as all combination between any substances with oxygen, and reduction as the reverse reaction, as the lost of oxygen from a substance. • Nowadays, Oxidation is defined as the process of losing electrons, and Reduction as the reverse process, of gaining electrons. For example:
Cu → Cu2‐ ± 2 e‐ oxidation 2 Ag‐ + 2 e‐ → 2 Ag reduction • Neither processes exists independently, which means that every oxidation process entails a reduction process, hecne the name, REDOX reactions.
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You Tube Video Chemical Reactions http://www.youtube.com/watch?v=ul4xRy8hcsQ
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Objectives • Identify and describe the definition and parts of a chemical reaction. • Understand and practice the balance of equations. • Identify and describe the Synthesis and Decomposition reactions. Note: All, or most, of the objectives will be covered during class time, however the student must be responsible for those objectives not covered or concluded.
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Vocabulary • • • • • •
Reactant Product Reversible Decomposition Synthesis Balancing
Note: Most of the vocabulary words will be covered during class time, however the student must be responsible for those words not covered or concluded.
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Link and Learn You can visit the following websites to improve your understanding on the present topic: • • • • •
http://bit.ly/2TOjh9 http://bit.ly/Iopos http://science‐learning2009.wikispaces.com http://learningandscience.blogspot.com http://libraryatstgeorge.blogspot.com
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Prepared by
Gerardo LAZARO Science Lead Teacher Email: glazaro@sanjorge.edu.pe Wiki: http://science‐learning2009.wikispaces.com Blog: http://learningandscience.blogspot.com Twitter: http://twitter.com/glazaro
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