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Reaction Rates

Chemical Collision Theory

For a chemical reaction to occur the chemicals or atoms or molecules must collide together.
Particles of matter are in constant motion and have kinetic energy. This motion enables the molecules
to collide. When they collide the particles can rearrange themselves into a new molecule.


The collisions are random as the particles can move in different ways.

Reactants and Products
In any chemical reaction there must be chemicals to initiate the reaction and chemicals that form as a
result of the reaction.
The chemicals that initiate the reaction are called the reactants and the chemicals that form as a result
of the reaction are called the products, e.g. the burning of methane:

Reaction Rates
The reaction rate is a measure of the time it takes to turn the reactants into the products.
The reaction rate can be measured by how much product is produced at regular time intervals.
Factors that effect the reaction rate:

• Surface area: This means increasing the surface area increases the reaction rate, i.e, crush the
compound into a powder if possible. This allows for more particle collisions to occur in a given
time, e.g. powdered coal on a fire will flare up into flames quickly.
• Concentration: Increasing concentration increases the reaction rate. This means there are more
particle to particle collisions, e.g. a concentrated acid dissolves a metal very quickly.
• Temperature: Increasing the temperature increases the reaction rate. This means the particles
are moving about more rapidly and therefore there are more collisions, e.g. heating the water will
mean the sugar dissolves more easily.
• Catalysts: This is a compound which speeds up a reactions without being used up itself, e.g. there are
many biological catalysts that speed up reactions in the cells of living organisms, such as enzymes.