# A student investigates how temperature affects the rate of a reaction between sodium thiosulfate solution and dilute hydrochloric acid. As the temperature of the sodium thiosulfate solution is increased from 20 °C to 60 °C, the reaction gets progressively faster. Explain, in terms of particles, why increasing the temperature causes the rate of reaction to increase.

> OCR A-Level Chemistry B: Salters (H433) — 5.2 Energy · Explain · 5 marks

> The reaction between sodium thiosulfate solution and dilute hydrochloric acid produces a yellow sulfur precipitate. The student measures how long it takes for the precipitate to obscure a cross marked on paper beneath the flask. At 20 °C the cross disappears after 90 seconds; at 60 °C it disappears after only 12 seconds.

## Mark scheme (5 marks)

1. Increasing temperature gives particles more kinetic energy
2. Particles move faster / collide more often (higher frequency of collisions)
3. A greater proportion of particles have energy equal to or greater than the activation energy
4. Therefore there are more successful collisions per unit time
5. So the rate of reaction increases (linking both reasons — frequency and proportion — to the faster rate)

## Key terms

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

## Related

- [Revision notes for OCR A-Level Chemistry B: Salters (H433)](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/a-student-investigates-how-temperature-affects-35b3382e) · Published by Druglandscape Ltd.