Investigating Chemical Reactions

• Chemical reactions are simply processes that involve chemical change.

• A chemical change is one in which new substances are formed.

• Mass is conserved in a chemical reaction (Law of Conservation of

Mass).

• This is true since the number of atoms of each element is conserved in a

chemical reaction.

• Chemical equations are used to describe chemical reactions.

9CHAPTER

Investigating Chemical Reactions

• There are six common types of chemical reactions.

• Chemists are able to use these patterns to predict the products of

common reactions.

• Some chemical reactions are slow, some are fast.

• The rate of a chemical reaction is affected by various factors.

• These factors include temperature, reactant concentration, surface

area of reactants, and the presence of a catalyst.

9CHAPTER

Investigating Chemical Reactions

Activity

• In groups of two or three, brainstorm 3–4 different clues that may indicate when a chemical change is occurring. What might you sense—see, hear, feel, smell, etc.?

• Using your clues, determine if a physical or chemical change is taking place when

• food colouring is added to water.

• wax cools into a solid.

• water forms bubbles when boiling.

• steam releases heat when condensing.

• What do you think must occur at the molecular level for a change to be a chemical change?

• See page 232 in the textbook for the difference between a physical and chemical change.

9CHAPTER

Investigating Chemical Reactions9

Key Ideas

• Chemical reactions are processes that involve chemical change

and obey the Law of Conservation of Mass.

• Chemical equations are used to describe chemical reactions.

• There are six common types of chemical reactions.

• Chemists are able to predict the products of common reactions.

• The rate of a chemical reaction is affected by various factors.

CHAPTER

• Chemical reactions are simply processes that involve

chemical change.

• A chemical change is one in which new substances are

formed.

• A chemical equation uses chemical formulas to

describe the chemicals that react (the reactants) and

those that are produced (the products).

• Mass is conserved in a chemical reaction (Law of

Conservation of Mass).

• This is true since the number of atoms of each element

is conserved in a chemical reaction.

Describing Chemical Compounds9.1

VOCABULARY

chemical reactions

chemical equation

reactants

products

Law of Conservation

of Mass

Writing and Balancing Chemical Equations9.2

VOCABULARY

skeleton equation

balanced equation

• Chemical equations are used to describe chemical reactions.

• Coefficients in a chemical equation describe the number of molecules of each compound or element, whereas subscripts describe the number of atoms of each element.

• Balancing an equation involves changing the coefficients as required throughout the equation so that atoms are conserved. Subscripts are never changed.

• For example when the number of atoms of the reactant element(s) are the same as the number of atoms of the product element(s), the equation is balanced.

Types of Chemical Reactions9.3

VOCABULARY

synthesis reaction

decomposition reaction

single replacement

reaction

double replacement

reaction

acid–base

neutralization

reaction

combustion reaction

• There are six types of chemical reactions.• Patterns exist in chemical reactions that allow most to

be classified as one of six types:

Types of Chemical Reactions9.3

VOCABULARY

synthesis reaction

decomposition reaction

single replacement

reaction

double replacement

reaction

acid–base

neutralization

reaction

combustion reaction

• Given the reactants for a reaction, you can often

predict the products that will form, as well as the

relative amounts of reactants and products based

on the patterns shown on the previous screen.

• For example:

• Predicting the reactants or products of a reaction

requires an understanding of reaction types,

chemical formula writing, and balancing equations.

Rates of Chemical Reactions9.4

VOCABULARY

reaction rate

kinetic molecular

theory

collision theory

catalyst

• Some chemical reactions are slow, some are fast.

• For example a car rusting is slow; a matchstick

burning is fast.

• The reaction rate of a chemical reaction is the

amount of reactant consumed per unit time or the

amount of product formed per unit time.

• It is the “speed” of the reaction.

• Reaction rate is explained by the collision theory,

which states that molecules must collide in order

to react.

• Collisions must also be effective, which means that

they must have sufficient energy for a reaction to

occur.

• Reaction rate can be increased by:

1. increasing the concentration of reactants 3. increasing the

temperature

2. increasing the surface area of reactants 4. adding a catalyst

Rates of Chemical Reactions9.4

VOCABULARY

reaction rate

kinetic molecular

theory

collision theory

catalyst