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Collision theory and catalysts
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Particles must collide with enough energy to react. Every factor that changes rate does so by changing collisions.
Collision theory
Particles react only when they collide with at least the activation energy.
Rate depends on the frequency of collisions and the proportion that are successful.
Rate depends on the frequency of collisions and the proportion that are successful.
Explaining the factors
Higher concentration or pressure: more particles in the same space, more frequent collisions.
Larger surface area: more particles exposed, more frequent collisions.
Higher temperature: particles move faster, so more frequent collisions, and more collisions have enough energy.
Larger surface area: more particles exposed, more frequent collisions.
Higher temperature: particles move faster, so more frequent collisions, and more collisions have enough energy.
Catalysts
A catalyst speeds up a reaction without being used up.
It provides an alternative pathway with a lower activation energy.
Enzymes are biological catalysts.
It provides an alternative pathway with a lower activation energy.
Enzymes are biological catalysts.
Explain why heating increases the rate of reaction.
- Particles gain kinetic energy and move faster.
- They collide more often.
- More collisions have at least the activation energy.
Answer: More frequent and more energetic collisions.
Reactions need collisions with at least the activation energy. Concentration, pressure and surface area increase collision frequency; temperature also makes collisions more energetic. Catalysts lower activation energy.
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