Chemistry 12 · Chemistry · Lesson 1.3
Collision theory
- Level
- Grade 12
- Reading time
- 11 min reading
- Review
- Last reviewed 2026-09-03
- Standard
- Accuracy standard
- Errata
Abstract
Why some collisions cause reactions and others do not.
What is collision theory?
Short answer
Collision theory explains reaction rates in terms of particle collisions. For a reaction to occur, particles must collide with enough energy (at least the activation energy) and in the correct orientation. Only a fraction of collisions meet both conditions. Anything that increases the frequency or energy of effective collisions — higher concentration, temperature, or a catalyst — speeds up the reaction.
Concept preview
What you will be able to do
- 01State collision theory and its two conditions
- 02Use the energy distribution to explain the effect of temperature
- 03Explain every rate factor in terms of successful collisions
Collision theory is the model that ties all the rate factors together. Its starting point is simple: for particles to react, they must first collide with one another. No collision, no reaction. But collisions alone are not enough — in a typical reaction, the vast majority of collisions produce no reaction at all. Only a small fraction, the successful (or effective) collisions, actually lead to products.
School Plan
Collision theory
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Related topics
Frequently asked questions
- What makes a collision effective?
- The particles must collide with at least the activation energy and in the right orientation to rearrange bonds.
- How does temperature affect collisions?
- Higher temperature raises particle speed, so collisions are more frequent and a greater fraction exceed the activation energy.