Chapter 7 NotesChapter 7 NotesChemical Reactions

Chapter 7.1 Describing ReactionsChapter 7.1 Describing Reactions ReactantsReactants – –

substances that undergo changesubstances that undergo change

ProductsProducts – – new substances formed as a result of that new substances formed as a result of that

changechange

Reactants Reactants Products Products

Chapter 7.1 Describing ReactionsChapter 7.1 Describing Reactions Chemical Equation – –

representation of a chemical reaction in which representation of a chemical reaction in which the reactants and products are expressed as the reactants and products are expressed as formulas.formulas. Ex) C + OEx) C + O22 CO CO22

Burning of CarbonBurning of Carbon

Figure 2

Burning of CarbonBurning of Carbon

Figure 2

Burning of CarbonBurning of Carbon

Figure 2

Chapter 7.1 Describing ReactionsChapter 7.1 Describing Reactions Law of Conservation of Mass – Law of Conservation of Mass –

mass cannot be created or destroyed in a mass cannot be created or destroyed in a chemical equation; it can only change formchemical equation; it can only change form

Chapter 7.1 Describing ReactionsChapter 7.1 Describing Reactions

In order to show that mass is conserved during a In order to show that mass is conserved during a reaction, a chemical equation must be BALANCED reaction, a chemical equation must be BALANCED (same # of atoms of each element on both sides)(same # of atoms of each element on both sides)

Coefficient – Coefficient – number written before the formulasnumber written before the formulas

change these to balance equationchange these to balance equation NEVER change subscriptsNEVER change subscripts

Balancing PracticeBalancing Practice

2

N=2H=4O=2

N=2H=4O=2

More Balancing ProblemsMore Balancing Problems

2 2

24

2 2

2 4 3

Chapter 7.2 Types of ReactionsChapter 7.2 Types of Reactions Synthesis – –

two or more substances react to form a single substancetwo or more substances react to form a single substance

Chapter 7.2 Types of ReactionsChapter 7.2 Types of Reactions

Decomposition – – a compound breaks a compound breaks

down into two or more down into two or more simpler substancessimpler substances

Chapter 7.2 Types of ReactionsChapter 7.2 Types of Reactions

Single Replacement – – one element takes the place of another element one element takes the place of another element

in a compoundin a compound

AB + C AB + C AC + B AC + Bp.202p.202

Chapter 7.2 Types of ReactionsChapter 7.2 Types of Reactions

Double Replacement – – two different compound exchange positive ions two different compound exchange positive ions

and form two new compoundsand form two new compounds

AB + CD AB + CD AD + CB AD + CB p. 203p. 203

Models of Models of Reactions Reactions The following drawings The following drawings represent reactants and represent reactants and products of three different products of three different chemical reactions.chemical reactions.

1.1. SynthesisSynthesis means means “putting something “putting something together.” Which together.” Which drawing represents drawing represents a synthesis a synthesis reaction? Explain reaction? Explain your answer.your answer.

Models of Models of Reactions Reactions The following drawings The following drawings represent reactants and represent reactants and products of three different products of three different chemical reactions.chemical reactions.

2.2. DecompositionDecomposition means “taking means “taking something apart.” something apart.” Which drawing Which drawing represents a represents a decomposition decomposition reaction? Explain reaction? Explain your answer.your answer.

Models of Models of ReactionsReactions The following drawings The following drawings represent reactants and represent reactants and products of three different products of three different chemical reactions.chemical reactions.

3.3. ReplacementReplacement means “something means “something taking the place of taking the place of another.” Which another.” Which drawing represents drawing represents a replacement a replacement reaction? Explain reaction? Explain your answer. your answer.

Chapter 7.2 Notes Types of ReactionsChapter 7.2 Notes Types of Reactions

Other types of Reactions:Other types of Reactions: CombustionCombustion – –

a substance reacts rapidly with oxygen, producing a substance reacts rapidly with oxygen, producing heat and lightheat and light

Oxidation-Reduction (Redox)Oxidation-Reduction (Redox) – – electrons are transferred from one reactant to electrons are transferred from one reactant to

anotheranother OxidationOxidation – –

process in which an element process in which an element losesloses electrons during a electrons during a chemical reactionchemical reaction

ReductionReduction – – process in which an element process in which an element gainsgains an electrons an electrons

during a chemical reactionduring a chemical reaction

Chapter 7.2 Notes Types of ReactionsChapter 7.2 Notes Types of Reactions

Chemical Energy – Chemical Energy – energy stored in the chemical bonds of a energy stored in the chemical bonds of a

substancesubstance Breaking Bonds = required energyBreaking Bonds = required energy Forming Bonds = released energyForming Bonds = released energy

Exothermic Reaction – Exothermic Reaction – releases energy to its surrounding – formation releases energy to its surrounding – formation

of bondsof bonds Endothermic Reaction – Endothermic Reaction –

absorbs energy from its surroundings – absorbs energy from its surroundings – breaking of bondsbreaking 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 ReactionsChapter 7.2 Notes Types of Reactions

Law of Conservation of Energy – – energy cannot be created or destroyed; it can energy cannot be created or destroyed; it can

only change formonly change form The amount of energy in the universe is The amount of energy in the universe is

constant.constant.

Activation Energy –– The amount of energy required to start a The amount of energy required to start a

chemical reaction.chemical reaction.

Chapter 7.3 Notes Types of ReactionsChapter 7.3 Notes Types of Reactions

Reaction Rate – Reaction Rate – rate at which reactants change into products over rate at which reactants change into products over

timetime

Factors that affect reaction rates:Factors that affect reaction rates: 1. Temperature1. Temperature

increase the temperature, the reaction rate will increase; the increase the temperature, the reaction rate will increase; the opposite is also trueopposite is also true

2. Surface Area2. Surface Area increase surface area, the reaction rate will increaseincrease surface area, the reaction rate will increase

3. Stirring3. Stirring if you stir something, it will react fasterif you stir something, it will react faster

Chapter 7.2 Notes Types of ReactionsChapter 7.2 Notes Types of Reactions

Factors that affect reaction rates (Cont):Factors that affect reaction rates (Cont): 4. Concentration4. Concentration

if you increase the concentration, the reaction rate will if you increase the concentration, the reaction rate will increaseincrease

5. Catalyst – speeds up chemical reactions without taking part in speeds up chemical reactions without taking part in

the reaction itselfthe reaction itself Ex) enzymes that speed up digestionEx) enzymes that speed up digestion

6. 6. Inhibitors - slows down or stops chemical reactions from slows down or stops chemical reactions from

happeninghappening Ex) preservatives in foodEx) preservatives in food

Rates of reaction video

Chapter 7.2 Notes Types of ReactionsChapter 7.2 Notes Types of Reactions

Factors that affect reaction rates (Cont):Factors that affect reaction rates (Cont): 5. Catalyst – 5. Catalyst –

Which reaction requires the least amount of energy to activate?

Chapter 7.2 Notes Types of ReactionsChapter 7.2 Notes Types of Reactions

Equilibrium – Equilibrium – a state in which the forward and reverse paths a state in which the forward and reverse paths

of a change take place at the of a change take place at the same ratesame rate

Physical equilibrium – Physical equilibrium – both forward and reverse changes occur both forward and reverse changes occur

simultaneouslysimultaneously Ex) water condensing and Ex) water condensing and

evaporating at the same rateevaporating at the same rate

Chapter 7.2 Notes Types of ReactionsChapter 7.2 Notes Types of Reactions

Reversible reaction – Reversible reaction – reaction in which the conversion of reactants reaction in which the conversion of reactants

into products and the conversion of products into products and the conversion of products into reactants can happen at the same timeinto reactants can happen at the same time

Chemical equilibrium – Chemical equilibrium – forward and reverse chemical changes forward and reverse chemical changes

occur simultaneouslyoccur simultaneously Factors affecting chemical equilibrium:Factors affecting chemical equilibrium:

1.1. TemperatureTemperature2.2. PressurePressure3.3. ConcentrationConcentration

Back

Back

Back

Back

Back

Back

Back

Back

Back

Back