When materials are heated, they expand. Temperature increases, leading to increase in kinetic energy. This expansion happens because the molecules move/vibrate faster, which causes them to move further apart. This separation of the molecules makes the substance bigger. Molecules itself do not expand, the space in between them expands.
When heated (at constant pressure)
| Solid | Liquid | Gas | |
|---|---|---|---|
| When heated (at constant pressure) | Molecules gain energy & vibrate more. Expands slightly | Molecules vibrate & move about more vigorously Expands more than solids | Move even more randomly at higher speed, colliding with one another and with the walls of containers. Expands significantly |
Applications: Thermometers, Temperature-activated switches
Consequences
- Buckling - The expansion of solid materials (metal railway tracks, road surfaces, bridges) can cause them to buckle if they get too hot. Gaps built in to create space for the expansion to happen without causing damage.
Specific heat capacity
- Specific heat capacity – The energy required per unit mass per unit temperature increases.
∆E=mc∆θ
Change in thermal energy (J) = mass (kg) x specific heat capacity (J/kg°C) x change in temperature (°C)
Apparatus to measure heat capacity of a solid: thermometer, heater, power supply, ammeter, voltmeter, solid.
Melting, boiling and evaporation
Melting and boiling occurs when particles gain energy, without a change in temperature. Condensation and solidification occurs when particles lose energy. Evaporation occurs when energetic particles escape from the surface of a liquid. Evaporation causes cooling of a liquid.
| Boiling | Evaporating | |
|---|---|---|
| Where | Occurs throughout the liquid. | Occurs at the surface of a liquid. |
| When | Happens at the boiling point of the liquid. | Happens at any temperature. |
Pure water melting point = 0°C, boiling point = 100°C
Evaporation increases when: temperature increases, surface area increases, air movement over the surface increases.