States of Matter & Changes of State
Section: Thermal Physics | Syllabus: Cambridge IGCSE Physics (0625)
States of Matter
Matter exists in three states: solid, liquid and gas. Each state has its own distinguishing shape, volume, flow and compressibility.
- Solids
- have a definite shape
- have a definite volume
- cannot flow
- are not compressible
- Liquids
- have no definite shape - they take the shape of their container
- have a definite volume
- are able to flow
- are not compressible
- Gases
- have no definite shape - they take the shape of their container
- have no definite (fixed) volume - they fill their container
- are able to flow
- are highly compressible
Properties of Solids, Liquids and Gases - Summary
| Property | Solid | Liquid | Gas |
|---|---|---|---|
| Shape | Definite | No definite shape | No definite shape |
| Volume | Definite | Definite | No fixed volume |
| Flow | Cannot flow | Can flow | Can flow |
| Compressibility | Not compressible | Not compressible | Highly compressible |
Changes of State
- When a substance changes state, the number of particles in it does not change, so its mass stays the same - only the energy of the particles changes
- Changes of state are physical changes, so they are reversible
Melting and Freezing
- Melting - a solid changes into a liquid (e.g. ice → water)
- Freezing - a liquid changes into a solid (e.g. water → ice)
Boiling and Condensing
- Boiling - a liquid changes into a gas (also called evaporating)
- Condensing - a gas changes into a liquid
The four changes of state: melting, freezing, boiling and condensing
- Only these four changes of state are required - a direct change between a solid and a gas is not required
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