# Explain, in terms of particles, what happens to the internal energy of a substance when it melts, and why the temperature of the substance does not change during melting.

> WJEC A-Level Physics (Wales) — 2.3 Capacitance (A-Level only) · Explain · 5 marks

> A solid substance is heated steadily until it has completely melted. During the melting process, the temperature of the substance remains constant even though energy is continuously being supplied.

## Mark scheme (5 marks)

1. During melting, energy is supplied to the particles (of the substance)
2. The energy supplied increases the potential energy of the particles (as bonds/intermolecular forces are broken/overcome)
3. The kinetic energy of the particles does not increase during melting
4. Temperature is a measure of the average kinetic energy of the particles, so temperature does not change if kinetic energy does not change
5. The internal energy increases during melting because internal energy is the sum of kinetic and potential energies of the particles, and potential energy has increased

## Key terms

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

## Related

- [Revision notes for WJEC A-Level Physics (Wales)](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)

---
Source: [GradeNine](https://www.gradenine.co.uk/q/explain-in-terms-of-particles-what-4c3dbe68) · Published by Druglandscape Ltd.