# Explain why the temperature of a substance does not change while it is melting, even though energy is continuously being supplied to it.

> Pearson Edexcel International GCSE Physics (4PH1) — 5.2 Change of state · Explain · 4 marks

> A block of a pure substance is placed in a heated container. Energy is supplied to the substance at a constant rate. The substance begins to melt, but a thermometer placed in the container shows no rise in temperature during this time.

## Mark scheme (4 marks)

1. Energy supplied goes towards separating / freeing the molecules from each other (breaking the intermolecular forces between molecules)
2. The energy supplied does NOT increase the kinetic energy of the molecules
3. Temperature is a measure of the average kinetic energy of the particles, so if kinetic energy does not increase, temperature does not rise
4. The internal energy of the substance still increases (potential energy of the molecules increases) during the change of state

## Key terms

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

## Related

- [Revision notes for Pearson Edexcel International GCSE Physics (4PH1)](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-a-d96b8dd3) · Published by Druglandscape Ltd.