Controlling the Rate of
Chemical Reactions or
Going Into Solution
A chemical reaction is a process in which
the physical and chemical properties of
the reactants change as new substances
(products) with different physical and
chemical properties are formed.
Observing a Chemical
Magnesium and oxygen combine to form magnesium oxide.
Characteristics of a Chemical
• Chemical reactions always involve a change
• Energy is either absorbed (endothermic
reaction) or released (exothermic reaction)
during a chemical reaction.
Energy & Reactions
• The rate of a reaction is a measure of how
quickly reactants turn into products.
• Chemical reactions require energy to break
the chemical bonds of the reactants so that
the atoms can begin to form the new
chemical bonds of the products.
• The activation energy is the minimum
amount of energy needed to start a chemical
All chemical reactions need a
certain amount of activation energy
to get started.
In this type of reaction, the energy of the products is less than the
energy of the reactants.
In this type of reaction, the energy of the products is greater than
the energy of the reactants.
Factors that Increase the
Rate of a Chemical Reaction
Use of a Catalyst
#1 Surface Area
The surface area of a reactant influences the rate of reaction by -
• allowing more particles of a substance to
• The more particles are exposed, the faster the
reaction will happen.
To dissolve the particles at the center of the object you must
first dissolve each of the layers around the center. This
process will take a long amount of time to complete.
If your were to break apart the substance into smaller pieces,
the reaction would take less time.
Less surface area = Greater surface area =
slower reaction time faster reaction time
When you heat a substance, its particles move faster. Faster moving
particles increase the reaction rate in two ways:
• particles come in contact more often, which
increases the chance of a reaction
• faster moving particles get over the AE
“hump” easier due to increased energy
• decreasing the temperature slows down
+ - + -
Concentration is the amount of a substance in a given volume.
Increasing the concentration of
reactants supplies more particles to
Other Factors that Affect
• A catalyst is a material that increases the rate
of a reaction by lowering the activation
• An inhibitor is a material used to decrease
the rate of a chemical reaction.