Collision Theory

Reactions can only occur when reacting particles collide with enough energy.

This energy is called the activation energy. Most collisions do not result in reaction.

Increasing the concentration of reactants increase the number of particles available to react.

More collisions occur in a given time. Therefore the rate of reaction is increased. 

Dividing a solid into smaller pieces increases the surface area. If there is a larger surface available for particles to collide with there will be more collisions. Therefore the rate of reaction is increased.

Increasing the temperature of the reaction increases the speed at which particles move. There are more collisions in a given time and so the rate of reaction is increased.

On average, the collisions also have a higher energy. This means that a higher proportion of the collisions are successful and lead to reaction. Therefore the rate of reaction is increased

Catalyst provide a different route for the reaction to happen. This route has a lower activation energy. This means that more of the collisions will be effective. The rate of reaction is increased.