Catalysts (AQA GCSE Chemistry): Revision Notes
Catalysts
What are catalysts?
Catalysts are special chemicals that make reactions happen faster. The key thing to remember is that they don't get used up in the reaction. They help the reaction along but stay unchanged at the end.
Think of a catalyst like a helpful friend who shows you a shortcut - they help you get there faster, but they don't disappear in the process!
How catalysts work
Catalysts work by lowering the activation energy needed for a reaction to start. Here's what happens:
- Without a catalyst: Particles need lots of energy to react successfully
- With a catalyst: Particles need less energy to react, so more collisions are successful
The catalyst provides an alternative pathway for the reaction. This pathway has lower activation energy, making it easier for reactant particles to turn into products.
This alternative pathway is like finding a mountain pass instead of climbing over the peak - it's still the same journey, but much easier to complete!
Key properties of catalysts
Catalysts are specific
- Different reactions need different catalysts
- One catalyst won't work for every reaction
Catalysts provide alternative routes
- They give the reaction an easier path to follow
- Lower activation energy means faster reactions
Biological catalysts are called enzymes
In living things, catalysts are called enzymes. They speed up important reactions in our bodies, from digesting food to building proteins.
Example: hydrogen peroxide breakdown
Worked Example: Hydrogen Peroxide Decomposition
A common example uses hydrogen peroxide decomposing to make water and oxygen:
Comparison of reaction rates:
- Without catalyst: Reaction happens very slowly
- With manganese(IV) oxide (MnO₂): Reaction happens much faster
- The MnO₂ is still there at the end - it hasn't been used up
Testing for catalysts
How to Prove Something is a Catalyst
To prove something is a catalyst, you need to show it isn't used up:
- Weigh the solid at the start of the reaction
- Let the reaction happen completely
- Filter and dry the solid that remains
- Weigh it again - it should have the same mass
If the mass is the same, it proves the substance is a catalyst because it hasn't been consumed.
Summary
Key Points to Remember:
- Catalysts speed up reactions but don't get used up
- They lower activation energy by providing an easier pathway
- Different reactions need different catalysts - they are specific
- You can prove something is a catalyst by showing its mass doesn't change
- In living things, catalysts are called enzymes