Download (the products). Mass is conserved in a chemical reaction

9.1
Describing Chemical Compounds
• 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.
VOCABULARY
chemical reactions
chemical equation
reactants
products
Law of Conservation
of Mass
9.2
Writing and Balancing Chemical
Equations
• 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.
VOCABULARY
skeleton equation
balanced equation
9.3
Types of Chemical Reactions
• There are six types of chemical reactions.
• Patterns exist in chemical reactions that allow most to
be classified as one of six types:
VOCABULARY
synthesis reaction
decomposition reaction
single replacement
reaction
double replacement
reaction
acid–base neutralization
reaction
combustion reaction
9.3
Types of Chemical Reactions
• 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:
VOCABULARY
synthesis reaction
decomposition reaction
single replacement
reaction
double replacement
reaction
acid–base neutralization
reaction
combustion reaction
• Predicting the reactants or products of a reaction
requires an understanding of reaction types,
chemical formula writing, and balancing equations.
9.4
Rates of Chemical Reactions
• 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.
VOCABULARY
reaction rate
kinetic molecular
theory
collision theory
catalyst
9.4
Rates of Chemical Reactions
• 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.
VOCABULARY
reaction rate
kinetic molecular
theory
collision theory
catalyst
• 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
CHAPTER
9
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.
CHAPTER
9
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.
CHAPTER
9
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.
CHAPTER
9
Investigating Chemical Reactions
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.