# When a substance is heated at a constant rate, its temperature does not always rise continuously. Explain why the temperature of a substance remains constant during a change of state, even though energy is still being supplied.

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

> A block of ice is heated at a constant rate. As it melts, a thermometer placed in the mixture shows a steady reading, even though the heater continues to supply energy.

## Mark scheme (4 marks)

1. Energy supplied goes towards separating the particles / 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 energy supplied increases the potential energy of the molecules / the internal energy of the system increases due to an increase in potential energy

## Key terms

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

## 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/when-a-substance-is-heated-at-2fe1102c) · Published by Druglandscape Ltd.