Rates of Reaction


Collision Title

Rates of Reaction

Collision Theory
(Kinetic Theory)

The speed at which a reaction proceeds can be explained by using the collision theory.

What must first happen for a chemical reaction to take place? Well......................!

Particles don't Collide
No Reaction

No Reaction


Particles Collide but are not moving fast enough
No Reaction

Fast moving Particles Collide

1. The reacting particles must collide with each other

2. 'head on'

3. with enough energy (known as the activation energy) to break existing bonds

4. and with the correct orientation to bring reactive sites close together

5. to form new bonds


Relating The Theory To The Factors Affecting Rate


More Collisions Increase The Rate of Reaction

The rate of a Reaction Depends on Four Factors:

1.   Concentration    -    (or PRESSURE FOR GASES)

2.   Temperature

3.   Catalyst

4.   Size of Particles    -    (or SURFACE AREA)


Rise in Concentration - (or PRESSURE FOR GASES) increases the the number of collisions

If the solution is made more concentrated (or pressure is increased in the case of gases), then the  number of reacting particles are increased in a unit volume.  Having more particles results in more collisions, which leads to faster a rate of reaction i.e. reaction finishes in a quicker time.


Low Concentration

High Concentration


Rise in Temperature increases the number of collisions


Change in temperature alters the kinetic energy of reacting particles and hence the number of successful collisions with enough energy to break existing bonds and make product particles. The minimum energy needed to break existing bonds is called the ACTIVATION ENERGY (EA).

Increasing the temperature of reacting particles results in:

a) increases the range of kinetic energies;

b) increases the average kinetic energy;

c) increases the number of particles with more than the activation energy (see graphs below). 


Graph 1 Graph 2


 When the temperature of the reacting particles is increased they all start to move a lot faster. As a result of their quikness they have more collisions.

Low Temperature

High Temperature



Tags:Rates of Reaction, Collision Theory, Kinetic Theory, Catalyst



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