2.1.1 States of matter
- Syllabus
- 0625–2026–2027
- Topic
- 2.1.1
- Level
- —
Learning objectives
Distinguish solids, liquids and gases
A state of matter can be distinguished by whether it keeps its own shape, keeps its own volume and can be compressed easily.
| State | Shape | Volume | Compression and flow |
|---|---|---|---|
| solid | fixed shape | fixed volume | difficult to compress; does not flow |
| liquid | takes the shape of the part of its container it occupies | fixed volume | difficult to compress; flows |
| gas | no fixed shape; spreads to fill its container | no fixed volume; expands to fill the container | easily compressed; flows |
If a sample takes its container's shape, it could be a liquid or a gas. Decide between them by asking whether it keeps a fixed volume: a liquid does, while a gas fills all available space.
Shape alone is not enough to distinguish a liquid from a gas. This card describes observable bulk properties only; particle arrangement, separation and motion belong to the next Topic.
Name changes of state in both directions
A change of state changes whether a substance is solid, liquid or gas. Name the process from its starting state and finishing state.
| From | To | Name | Energy direction |
|---|---|---|---|
| solid | liquid | melting | energy is supplied |
| liquid | solid | freezing or solidification | energy is removed |
| liquid | gas | boiling or evaporation | energy is supplied |
| gas | liquid | condensation | energy is removed |
Learn the reverse pairs: melting ↔ freezing/solidification, and boiling/evaporation ↔ condensation. Water droplets forming outside a cold glass are produced by condensation of water vapour in the surrounding air; they do not leak through the glass.
Do not swap the direction: melting is solid to liquid, not liquid to solid; condensation is gas to liquid, not liquid to gas. Direct solid-to-gas and gas-to-solid changes are explicitly not required by this syllabus objective.