# Activation energy [Higher tier only]

Activation energy is the minimum energy needed for ‘successful collisions’ where atoms within the reactants rearrange to form products. It can be represented on an energy level diagram.

The diagram shows that when a catalyst is used, the activation energy is reduced. This makes more of the collisions successful at a given temperature. So a catalyst increases the rate of reaction by lowering the minimum energy required for ‘successful collisions’.

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