Collision Theory & Activation EnergyOxford AQA IGCSE Chemistry: Revision notes
Section 1
What does collision theory state?
Collision theory explains why chemical reactions occur, and why some reactions are faster than others. It states that a chemical reaction can only happen when reacting particles collide with each other, and they collide with sufficient energy to react.
Section 2
Do all collisions cause a reaction?
No. Particles are constantly moving and colliding, but most collisions do not result in a reaction — they are called unsuccessful collisions. Only collisions where the particles have enough energy, arranged correctly, lead to a reaction taking place; these are called successful collisions.
Simply saying particles 'need to collide' is not enough for full marks — you must also state that they need sufficient energy to react.
Section 3
What is activation energy?
The activation energy is the minimum amount of energy that particles must have when they collide in order to react. If colliding particles have less energy than the activation energy, no reaction occurs, no matter how many times they collide.
Think of activation energy as a hill that reactants must be pushed over before they can roll down into products — particles without enough energy simply bounce back without getting over the hill.
Section 4
How does increasing the rate of successful collisions increase reaction rate?
Anything that increases either the frequency of collisions (how often particles collide) or the energy of collisions (how many collisions have enough energy to be successful) will increase the rate of reaction, because more successful collisions happen per second.
Must Know
- Collision theory: particles must collide, and collide with enough energy, for a reaction to occur
- Activation energy is the minimum energy needed for particles to react on collision
- Only successful collisions (sufficient energy) result in a reaction
- Increasing the frequency of collisions increases the rate of reaction
- Increasing the proportion of collisions with enough energy also increases the rate of reaction
That's the notes covered.
Carry on to the next subtopic.