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.

 3.

Surface Area
increase surface area, the reaction rate will increase
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:
1. Temperature
2. Pressure
3. Concentration
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