States of matter and changes of state · Year 4
Everything around us is a solid, a liquid or a gas. Solids keep their shape, liquids flow and take the shape of their container, and gases spread out to fill any space. Heating and cooling change one state into another, and these changes drive the water cycle.
Key facts
- Solids: fixed shape and volume. Liquids: fixed volume, flow, take the container’s shape. Gases: fill the container and can be squashed.
- Melting: solid → liquid. Freezing: liquid → solid. Evaporating/boiling: liquid → gas. Condensing: gas → liquid.
- A substance melts at its melting point and boils at its boiling point; water: 0°C and 100°C.
- During a change of state the temperature stays the same.
- Evaporation happens at the surface at any temperature; it is faster when warm, windy, and with a large surface area.
- Mass is conserved when a substance changes state or dissolves.