# Changes of state

Melting, freezing, boiling, condensing and subliming change the state without changing the substance. Energy goes in or out, but the temperature stays flat while it happens.

Physics (school) · Part 04: Particles and heat · Card 3 of 8 · Last updated 2026-10-19

## Analogy

Ice in a drink stays at 0 degrees until it has all melted.

## Example

**Water**

Melts at 0 degrees C.
Boils at 100 degrees C.
While it melts or boils, the
temperature stays constant.

## In practice

The mass stays the same through any change of state, because no particles are lost.

## Practice

### Flashcards

- **What happens to temperature while a substance melts?** It stays constant while energy breaks the bonds.

## Questions people ask

### Why does the temperature stay constant while ice melts?

The energy you add is used to break the bonds holding particles in the solid, not to make them move faster. Temperature only rises once all the ice has melted. The same happens during boiling, where energy pulls the particles apart instead of raising the temperature.

### Is a change of state a chemical change?

No, it is a physical change. The particles stay the same and no new substance is made. Water vapour is still H2O, and freezing it again gives back ice. The change can be reversed simply by adding or removing heat energy.

## Related concepts

- [Density](https://studyvisually.com/learn/science/physics-school/physics-school-part-4/physics-school-part-4-concept-1)
- [States of matter](https://studyvisually.com/learn/science/physics-school/physics-school-part-4/physics-school-part-4-concept-2)
- [Specific heat capacity](https://studyvisually.com/learn/science/physics-school/physics-school-part-4/physics-school-part-4-concept-4)
- [Conduction](https://studyvisually.com/learn/science/physics-school/physics-school-part-4/physics-school-part-4-concept-5)

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