# Explain why two reactions with identical activation energies can have different rates at the same temperature.

> IB DP Chemistry Standard Level (2023 syllabus) — R2.2 How fast? The rate of chemical change · Explain · 4 marks

> The rate of a chemical reaction depends on both the frequency of collisions between reactant particles and the proportion of those collisions that have sufficient energy to result in a reaction.

## Mark scheme (4 marks)

1. Rate depends on the frequency of successful collisions, not just the proportion of particles with energy ≥ Ea.
2. If activation energies are the same, the same fraction/proportion of collisions will have energy ≥ Ea at a given temperature.
3. The reactions can differ in the frequency of collisions between reactant molecules, for example due to different concentrations or different molecular sizes/masses.
4. A higher collision frequency means more successful collisions per unit time even if the proportion with energy ≥ Ea is the same, so the rate is higher.

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-two-reactions-with-identical-c20b26ee) · Published by Druglandscape Ltd.