# Explain why the temperature of boiling water does not rise above 100 °C even when a kettle continues to supply energy to it.

> OCR GCSE Physics A: Gateway Science (J249) — P1.2 Changes of state · Explain · 4 marks

> A chef notices that no matter how long a pan of water is left boiling on a high flame, a thermometer placed in the water always reads 100 °C. The chef wonders why the extra energy from the flame does not make the water hotter.

## Mark scheme (4 marks)

1. The energy supplied during boiling is used to change state (from liquid to vapour/gas), not to raise temperature
2. This energy is called latent heat (specific latent heat of vaporisation)
3. During a change of state the temperature remains constant
4. The intermolecular forces between particles must be overcome/broken for the particles to escape into the vapour state, and this requires energy

## Key terms

- [temperature](https://www.gradenine.co.uk/glossary/temperature)

## Related

- [Revision notes for OCR GCSE Physics A: Gateway Science (J249)](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/explain-why-the-temperature-of-boiling-8953f7b6) · Published by Druglandscape Ltd.