Rates of reaction and collision theory
What changes the speed of a reaction and why, using collision theory.
Collision theory
Particles react only when they collide with enough energy. The minimum energy needed is the activation energy. More successful collisions per second means a faster reaction.
What speeds it up
Temperature: particles move faster and more collisions have enough energy. Concentration or pressure: more particles in the same space, so more frequent collisions. Surface area: smaller pieces expose more particles. Catalyst: provides a route with a lower activation energy.
Measuring rate
Measure how quickly a product forms or a reactant is used up, for example gas volume every 10 seconds. Rate = amount changed ÷ time.
✏️ Worked example
Why does powdered calcium carbonate react faster with acid than lumps?
The powder has a much larger surface area, so more particles are exposed and collisions are more frequent.
🧠 Test yourself
What is activation energy?
The minimum energy particles need to react when they collide.
Does a catalyst get used up?
No, it is not used up.
Name two ways to speed up a reaction between a gas and a solid.
E.g. increase pressure, increase temperature, use a powder, add a catalyst.
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