# Catalyst

A catalyst speeds up a reaction without being used up. It gives the reaction a new path with a lower activation energy. It does not change ΔH or the final equilibrium position, only how fast equilibrium is reached.

Chemistry (university) · Part 06: Chemical kinetics · Card 9 of 9 · Last updated 2026-10-19

## Analogy

A tunnel through a mountain: it doesn't change where you start or end, but the trip is far easier.

## Example

**Effect on energy**

Ea (no catalyst): 100 kJ/mol
Ea (catalyst): 60 kJ/mol
ΔH unchanged
Both forward and reverse speed up

## In practice

Catalytic converters in cars use platinum and rhodium to turn toxic CO and NO into CO₂ and N₂.

## Practice

### Flashcards

- **Does a catalyst change the equilibrium position?** No. It only makes the reaction reach equilibrium faster.

### Interview questions

**Explain with collision theory why raising temperature and adding a catalyst both increase rate.**

- Temperature raises the fraction of molecules above Ea
- Catalyst gives a lower-Ea path
- Both raise the number of effective collisions
- Catalyst does not change ΔH

## Questions people ask

### Do enzymes work the same way as other catalysts?

Yes. Enzymes are biological catalysts, usually proteins. They lower the activation energy by holding reactants in the right position at the active site. They are very specific and work in mild conditions, but they follow the same rule: faster rate, same equilibrium.

### What is the difference between homogeneous and heterogeneous catalysts?

A homogeneous catalyst is in the same phase as the reactants, such as an acid dissolved in a liquid reaction. A heterogeneous catalyst is in a different phase, such as a solid metal surface catalysing gas reactions. Heterogeneous catalysts are easier to separate afterward.

## Related concepts

- [Collision theory](https://studyvisually.com/learn/science/chemistry-university/chemistry-university-part-6/chemistry-university-part-6-concept-6)

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