# A student investigates how changing the concentration of hydrochloric acid affects the rate of reaction with marble chips. Describe how the rate of reaction changes as the concentration of hydrochloric acid increases, and explain why this change occurs in terms of particles.

> AQA A-Level Chemistry (7405) — 3.1.9 Rate equations (A-Level only) · Describe and Explain · 5 marks

## Mark scheme (5 marks)

1. Rate of reaction increases as concentration of hydrochloric acid increases
2. Higher concentration means more particles (of hydrochloric acid / hydrogen ions) in the same volume
3. Particles collide more frequently / there are more frequent collisions
4. More collisions have (sufficient / the required) activation energy / more successful collisions
5. Therefore the rate of reaction increases because products are formed more quickly / more often

## Key terms

- [concentration](https://www.gradenine.co.uk/glossary/concentration)
- [rate of reaction](https://www.gradenine.co.uk/glossary/rate-of-reaction)

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](https://www.gradenine.co.uk/learn)
- [How to answer "Describe and 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/a-student-investigates-how-changing-the-2bf77411) · Published by Druglandscape Ltd.