Catalysts & Rate of ReactionsOxford AQA IGCSE Chemistry: Revision notes
Section 1
What is a catalyst?
A catalyst is a substance that changes (usually increases) the rate of a chemical reaction, but is not itself used up or chemically changed during the reaction. Because it is not consumed, the same particle of catalyst can be used again and again.
Section 2
Do all reactions need the same catalyst?
Different reactions need different catalysts — a catalyst that works well for one reaction may have no effect on another. For example, iron is used as a catalyst in the Haber process (making ammonia), while vanadium(V) oxide is used as a catalyst in the Contact process (making sulfuric acid).
Manganese(IV) oxide catalyses the decomposition of hydrogen peroxide, while it has no useful catalytic effect on most other reactions.
Section 3
How does a catalyst increase rate of reaction?
A catalyst works by providing an alternative reaction pathway that has a lower activation energy than the uncatalysed reaction. Because more particles have enough energy to react when less energy is needed, more successful collisions happen in a given time, so the rate of reaction increases.
Always describe a catalyst's effect as providing a 'different reaction pathway with lower activation energy' — simply saying it 'speeds up the reaction' will not gain full marks.
Section 4
Why are catalysts important in industry?
Catalysts are extremely important in industrial processes because they increase the rate of reaction, allowing lower temperatures to be used to achieve a useful rate. This reduces the energy costs of a process, which reduces the overall cost of production, since heating industrial reactors to very high temperatures uses large amounts of energy and money.
Must Know
- A catalyst increases the rate of reaction without being used up or chemically changed
- Different reactions require different, specific catalysts
- A catalyst works by providing a reaction pathway with lower activation energy
- Lower activation energy means more particles have enough energy to react on collision
- Catalysts reduce energy costs in industrial processes, making them cheaper to run
That's the notes covered.
Carry on to the next subtopic.