# Hand warmers are single-use packets used by hikers in cold weather. When a hand warmer is activated, a chemical reaction occurs inside the packet and the surface of the packet becomes warm to the touch. Explain why the packet becomes warm, using the terms bond breaking and bond making in your answer. Also state whether the overall energy change of this reaction is positive or negative, and justify your answer.

> OCR A-Level Chemistry A (H432) — 3.2 Physical chemistry · Explain · 5 marks

> Hand warmers are single-use packets used by hikers in cold weather. When a hand warmer is activated, a chemical reaction occurs inside the packet and the surface of the packet becomes warm to the touch.

## Mark scheme (5 marks)

1. Bond breaking is an endothermic process (energy is taken in to break bonds in the reactants)
2. Bond making is an exothermic process (energy is released when new bonds form in the products)
3. More energy is released in bond making than is taken in during bond breaking
4. Therefore energy is transferred to the surroundings, causing the temperature of the surroundings (the packet surface) to increase
5. The overall energy change is negative, because more energy is released than is taken in (net energy is transferred to surroundings in an exothermic reaction)

## Key terms

- [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 A-Level Chemistry A (H432)](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/hand-warmers-are-single-use-packets-used-12f28018) · Published by Druglandscape Ltd.