Chapter 7 Notes Chemical Reactions

Chapter 7.1 Describing Reactions Reactants – substances that undergo change Products – new substances formed as a result of that change Reactants  Products

Chapter 7.1 Describing Reactions Chemical Equation – representation of a chemical reaction in which the reactants and products are expressed as formulas. Ex) C + O2  CO2

Burning of Carbon Figure 2

Burning of Carbon Figure 2

Burning of Carbon Figure 2

Chapter 7.1 Describing Reactions Law of Conservation of Mass – mass cannot be created or destroyed in a chemical equation; it can only change form

Chapter 7.1 Describing Reactions In order to show that mass is conserved during a reaction, a chemical equation must be BALANCED (same # of atoms of each element on both sides) Coefficient – number written before the formulas change these to balance equation NEVER change subscripts

Balancing Practice   2 N=2 H=4 O=2 N=2 H=4 O=2

More Balancing Problems   2 2 4 2 2 2 2 4 3

Chapter 7.2 Types of Reactions Synthesis – two or more substances react to form a single substance

Chapter 7.2 Types of Reactions Decomposition – a compound breaks down into two or more simpler substances

Chapter 7.2 Types of Reactions Single Replacement – one element takes the place of another element in a compound AB + C  AC + B p.202

Chapter 7.2 Types of Reactions Double Replacement – two different compound exchange positive ions and form two new compounds AB + CD  AD + CB p. 203

Models of Reactions The following drawings represent reactants and products of three different chemical reactions. 1. Synthesis means “putting something together.” Which drawing represents a synthesis reaction? Explain your answer.

Models of Reactions The following drawings represent reactants and products of three different chemical reactions. 2. Decomposition means “taking something apart.” Which drawing represents a decomposition reaction? Explain your answer.

Models of Reactions The following drawings represent reactants and products of three different chemical reactions. 3. Replacement means “something taking the place of another.” Which drawing represents a replacement reaction? Explain your answer.

Chapter 7.2 Notes Types of Reactions Other types of Reactions: Combustion – a substance reacts rapidly with oxygen, producing heat and light Oxidation-Reduction (Redox) – electrons are transferred from one reactant to another Oxidation – process in which an element loses electrons during a chemical reaction Reduction – process in which an element gains an electrons during a chemical reaction

Chapter 7.2 Notes Types of Reactions Chemical Energy – energy stored in the chemical bonds of a substance Breaking Bonds = required energy Forming Bonds = released energy Exothermic Reaction – releases energy to its surrounding – formation of bonds Endothermic Reaction – absorbs energy from its surroundings – breaking of bonds

What type of reaction is this?

What type of reaction is this?

What type of reaction is this?

What type of reaction is this?

Chapter 7.2 Notes Types of Reactions Law of Conservation of Energy – energy cannot be created or destroyed; it can only change form The amount of energy in the universe is constant. Activation Energy – The amount of energy required to start a chemical reaction.

Chapter 7.3 Notes Types of Reactions Reaction Rate – rate at which reactants change into products over time Factors that affect reaction rates: 1. Temperature increase the temperature, the reaction rate will increase; the opposite is also true 2. Surface Area increase surface area, the reaction rate will increase 3. Stirring if you stir something, it will react faster

Chapter 7.2 Notes Types of Reactions Factors that affect reaction rates (Cont): 4. Concentration if you increase the concentration, the reaction rate will increase 5. Catalyst – speeds up chemical reactions without taking part in the reaction itself Ex) enzymes that speed up digestion 6. Inhibitors - slows down or stops chemical reactions from happening Ex) preservatives in food Rates of reaction video

Chapter 7.2 Notes Types of Reactions Factors that affect reaction rates (Cont): 5. Catalyst – Which reaction requires the least amount of energy to activate?

Chapter 7.2 Notes Types of Reactions Equilibrium – a state in which the forward and reverse paths of a change take place at the same rate Physical equilibrium – both forward and reverse changes occur simultaneously Ex) water condensing and evaporating at the same rate

Chapter 7.2 Notes Types of Reactions Reversible reaction – reaction in which the conversion of reactants into products and the conversion of products into reactants can happen at the same time Chemical equilibrium – forward and reverse chemical changes occur simultaneously Factors affecting chemical equilibrium: Temperature Pressure Concentration

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