Collision Theory

Collision theory provides the scientific explanation for why the rate of a chemical reaction changes when conditions are altered. It is a core part of the AQA GCSE Chemistry specification and underpins everything you have learned about factors affecting rate. This lesson explains the theory in full, introduces the concept of activation energy, and shows you how to use collision theory to explain experimental observations.

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The Basics of Collision Theory

Collision theory states that for a chemical reaction to occur, the reacting particles must:

1. Collide with each other
2. Collide with sufficient energy (at least the activation energy)
3. Collide with the correct orientation (Higher tier concept)

If either condition is not met, the collision is unsuccessful and no reaction takes place. The particles simply bounce apart.

Condition	What It Means
Collision occurs	The reacting particles must physically hit each other
Sufficient energy	The kinetic energy of the colliding particles must be equal to or greater than the activation energy
Correct orientation	The particles must be facing the right way so that bonds can break and reform