# A student mixes citric acid solution with sodium hydrogencarbonate powder. Bubbles are produced and the temperature of the mixture decreases. Explain why the temperature decreases, in terms of bond breaking and bond forming, and state what type of energy change this reaction represents.

> AQA A-Level Chemistry (7405) — 3.1.8 Thermodynamics (A-Level only) · Explain · 5 marks

## Mark scheme (5 marks)

1. Bonds in the reactants must be broken (to start the reaction)
2. Breaking bonds requires / absorbs energy (from the surroundings)
3. New bonds are formed in the products
4. The energy released when bonds form is less than the energy absorbed when bonds break
5. The reaction is endothermic

## Key terms

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

## Related

- [Revision notes for AQA A-Level Chemistry (7405)](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-mixes-citric-acid-solution-3b42c38b) · Published by Druglandscape Ltd.