# A student adds a small amount of citric acid powder to a glass of water and stirs it. The glass feels noticeably colder on the outside after the powder has dissolved and reacted. Explain why the glass feels colder, using your knowledge of endothermic reactions and bond breaking and bond making.

> OCR GCSE Chemistry A: Gateway Science (J248) — C3.1 Introducing chemical reactions · Explain · 4 marks

> Citric acid is a weak acid found naturally in lemons and limes. It is often used in fizzy drink powders.

## Mark scheme (4 marks)

1. The reaction is endothermic
2. Energy is taken in from the surroundings (the water/glass)
3. More energy is required to break bonds in the reactants than is released when bonds are formed in the products
4. This causes the temperature of the surroundings to decrease, so the glass feels colder

## Key terms

- [endothermic reaction](https://www.gradenine.co.uk/glossary/endothermic-reaction)
- [bond breaking](https://www.gradenine.co.uk/glossary/bond-breaking)
- [bond making](https://www.gradenine.co.uk/glossary/bond-making)

## Related

- [Revision notes for OCR GCSE Chemistry A: Gateway Science (J248)](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/a-student-adds-a-small-amount-ec8ae84e) · Published by Druglandscape Ltd.