Edexcel iGCSE Chemistry -3.12 Catalysts- Study Notes- New Syllabus
Edexcel iGCSE Chemistry -3.12 Catalysts- Study Notes- New syllabus
Edexcel iGCSE Chemistry -3.12 Catalysts- Study Notes -Edexcel iGCSE Chemistry – per latest Syllabus.
Key Concepts:
3.12 know that a catalyst is a substance that increases the rate of a reaction, but is chemically unchanged at the end of the reaction
3.12 Catalysts
Definition:
A catalyst is a substance that increases the rate of a reaction but is chemically unchanged at the end of the reaction.
Key Characteristics of Catalysts
- Increase the rate of reaction.
- Provide an alternative reaction pathway.
- Lower the activation energy.
- Are not used up in the reaction.
- Remain chemically unchanged at the end.
How Catalysts Work
A catalyst lowers the activation energy required for a reaction.
This means more particles have energy greater than activation energy.
Therefore, more successful collisions occur per second.
Example Reaction
Decomposition of hydrogen peroxide:
\( \mathrm{2H_2O_2(aq) \rightarrow 2H_2O(l) + O_2(g)} \)
Manganese dioxide \( \mathrm{MnO_2} \) acts as a catalyst.
- Oxygen is produced faster.
- The \( \mathrm{MnO_2} \) remains unchanged.
Catalyst and Energy Diagram (Concept)
- The activation energy is lower with a catalyst.
- The overall enthalpy change \( \Delta H \) is unchanged.
- Reactants and products energy levels remain the same.
| Feature | With Catalyst | Without Catalyst |
|---|---|---|
| Activation energy | Lower | Higher |
| Reaction rate | Faster | Slower |
| ΔH | Unchanged | Unchanged |
| Catalyst at end | Unchanged | Not present |
Example 1 (Conceptual):
Does a catalyst change the energy difference between reactants and products?
▶️ Answer/Explanation
No.
It only lowers activation energy.
The overall enthalpy change remains the same.
Example 2 (Application):
Why is manganese dioxide still present after decomposition of hydrogen peroxide?
▶️ Answer/Explanation
A catalyst is not used up.
It remains chemically unchanged.
Example 3 (Hard):
Explain fully how a catalyst increases the rate of reaction using collision theory.
▶️ Answer/Explanation
A catalyst provides an alternative reaction pathway.
This pathway has lower activation energy.
A greater proportion of particles have energy greater than activation energy.
More successful collisions occur per second.
The catalyst is chemically unchanged at the end.