AQA · GCSE · Combined Science
Course version: 8464 · Version from Sept 2018
Catalysts: Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy.
Reactions happen when particles collide with at least the activation energy, the minimum energy needed for a successful collision.
Study notes
From the checked teaching notes for this specification point.
The idea
Reactions happen when particles collide with at least the activation energy, the minimum energy needed for a successful collision. A catalyst increases the rate by providing a different pathway with a lower activation energy. On an energy profile, the reactants and products stay at the same energy levels, but the peak between them is lower, so a greater proportion of collisions has enough energy to react. For example, adding manganese(IV) oxide to hydrogen peroxide gives a lower-energy route, so oxygen is produced faster. The catalyst is not used up and does not change the overall energy change of the reaction; it only changes the route and therefore the rate.
What earns the marks
- A catalyst increases the rate of reaction by providing a different pathway.
- The different pathway has a lower activation energy than the uncatalysed route.
- Lower activation energy means a greater proportion of collisions have enough energy to react.
- The catalyst is not used up and does not change the overall energy change of the reaction.
- An energy profile can show the catalysed route with a lower peak between reactants and products.
Common mistakes and how to put them right
Saying the catalyst lowers the energy of the reactants or products.
Put it right by stating it lowers the activation energy of the pathway, not the energy levels of reactants or products.
Saying the catalyst gives particles more energy.
Put it right by stating it provides a different pathway with a lower activation energy.
Saying the catalyst changes the overall energy change.
Put it right by stating the energy change between reactants and products is unchanged.
Exam tips
- Use the phrase lower activation energy and link it to a greater proportion of successful collisions.
- Sketch or interpret an energy profile showing the catalysed peak lower than the uncatalysed peak.
- State that the catalyst is not used up and does not alter the overall energy change.
Try the lesson
The start of the Catalysts: Catalysts increase the rate of reaction by providing a different pathway for the reaction that has a lower activation energy. lesson, made from checked teaching notes for this specification point.
Have a go first
What effect does a catalyst have on the activation energy of a reaction?
Listen
Reactions happen when particles collide with at least the activation energy, the minimum energy needed for a successful collision. A catalyst increases the rate by providing a different pathway with a lower activation energy. On an energy profile, the reactants and products stay at the same energy levels, but the peak between them is lower, so a greater proportion of collisions has enough energy to react. For example, adding manganese(IV) oxide to hydrogen peroxide gives a lower-energy route, so oxygen is produced faster. The catalyst is not used up and does not change the overall energy change of the reaction; it only changes the route and therefore the rate. A strong answer earns marks for these points. A catalyst increases the rate of reaction by providing a different pathway. The different pathway has a lower activation energy than the uncatalysed route. Lower activation energy means a greater proportion of collisions have enough energy to react. The catalyst is not used up and does not change the overall energy change of the reaction. A common slip: Saying the catalyst lowers the energy of the reactants or products. Instead, stating it lowers the activation energy of the pathway, not the energy levels of reactants or products. Exam tip: Use the phrase lower activation energy and link it to a greater proportion of successful collisions.
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