# Explain why increasing the concentration of a reactant in solution increases the rate of a chemical reaction, with reference to collision theory and activation energy.

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

## Mark scheme (4 marks)

1. Increasing concentration increases the number of particles (solute molecules/ions) per unit volume.
2. A greater number density of particles leads to a higher frequency of collisions between reactant particles.
3. The proportion of collisions that exceed the activation energy is unchanged, but because there are more collisions overall, more collisions per unit time possess energy greater than or equal to the activation energy.
4. A greater number of successful collisions per unit time (collisions with correct orientation AND energy ≥ Ea) results in an increased rate of reaction.

## Key terms

- [collision theory](https://www.gradenine.co.uk/glossary/collision-theory)
- [activation energy](https://www.gradenine.co.uk/glossary/activation-energy)

## Related

- [Revision notes for IB DP Chemistry Higher 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-why-increasing-the-concentration-of-0ef7bcdd) · Published by Druglandscape Ltd.