Collision Theory & Rate of Reaction
Chemistry: Cambridge International GCSE Supplement, topic 6.2.1
Chemical Reactions: Collision Theory and Rate of Reaction
Reactions need particle collisions with sufficient energy and proper orientation. Rate rises with concentration or temperature, while catalysts lower Ea.
What is collision theory?
- Collision theory explains how chemical reactions occur when particles collide.
- The theory states that particles must collide to react.
- Collisions must have enough energy and proper orientation.
- Collision theory helps us understand the rate of reaction.
Number of particles per unit volume
- Reaction rate depends on the number of particles per unit volume.
- More particles in the same space mean more collisions occur.
- Increasing concentration usually increases reaction rate.
- Example: More hydrogen ions in acid speed up the metal reaction.
Frequency of collisions between particles
- Reaction rate increases with collision frequency.
- Particles collide more often when they move faster.
- Higher temperature makes particles move faster.
- More frequent collisions give more chances for reactions.
Kinetic energy and activation energy (Ea)
- Particles need enough kinetic energy to overcome activation energy, Ea.
- Activation energy is the minimum energy to start a reaction.
- Only collisions with energy ≥ Ea cause reaction.
- Increasing temperature raises kinetic energy, so more particles reach Ea.
Activation energy and reaction control
- Activation energy explains why some reactions are slow or fast.
- Catalysts lower activation energy, speeding up reactions.
- Without enough energy, particles bounce off without reacting.
- Understanding Ea helps control reaction rates in industry.
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What is activation energy (Ea)?