4.8 - Thermal Expansion
Thermal expansion
- When most substances are heated, they expand. This is called thermal expansion.
- It happens in solids, liquids and gases, as long as the surrounding pressure stays the same.
Why it happens
- Heating gives the particles more energy, so they move about more and push further apart, causing the substance to expand.
- Cooling reverses this: the particles lose energy, move less, settle closer together, and the substance contracts.
Why solids, liquids and gases expand by different amounts
- How much a substance expands depends on the forces of attraction between its particles.
- The stronger the forces, the less the particles can move apart, so the less the substance expands.
Comparing the three states
- Solids - Have the strongest forces between particles, so they expand the least.
- Liquids - Have weaker forces than solids, so they expand more than solids.
- Gases - Have almost no forces between particles, so they expand the most.
TermDefinition
Thermal expansionThe expansion of a substance when it is heated, caused by its particles moving further apart.