# A student adds a small amount of anhydrous calcium chloride to a test tube of water. The student notices that the outside of the test tube becomes noticeably warm. Explain why the temperature of the surroundings increases during this process, referring to bond breaking and bond making.

> OCR GCSE Chemistry A: Gateway Science (J248) — C3.2 Energetics · Explain · 4 marks

> Anhydrous calcium chloride is a white solid that dissolves readily in water. It is sometimes used as a drying agent and in self-heating food packaging.

## Mark scheme (4 marks)

1. Energy is required to break bonds in the reactants
2. Energy is released when new bonds are formed 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, so this is 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)
- [surroundings](https://www.gradenine.co.uk/glossary/surroundings)

## 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)

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Source: [GradeNine](https://www.gradenine.co.uk/q/a-student-adds-a-small-amount-677eb859) · Published by Druglandscape Ltd.