Thermal properties of matter

What the syllabus demands

• —Describe thermal expansion of solids, liquids and gases and its applications
• —Define specific heat capacity and use E = mcΔθ
• —Describe melting and boiling in terms of energy input without temperature change
• —Distinguish boiling from evaporation
• —Explain the factors that affect the rate of evaporation and its cooling effect

Definitions that earn marks

Clear definitions to practise — check your course mark scheme

Specific heat capacity

The energy required to raise the temperature of 1 kg of a substance by 1 °C.

Melting point

The temperature at which a solid changes to a liquid, with no temperature change while the change of state occurs.

Evaporation

The escape of the most energetic particles from the surface of a liquid, at any temperature below boiling — leaving the remaining liquid cooler.

The equations

More equations to practise: the IGCSE formula sheet.

Where the marks die

Common mistakes to check

1. 01

   Using the full temperature instead of the temperature change in E = mcΔθ. It is Δθ — final minus initial.

2. 02

   Saying temperature rises during melting or boiling. It does not: the energy input goes into breaking bonds between particles (increasing potential energy), not into raising temperature. Flat sections on a heating curve are worth marks only if you say why.

3. 03

   Confusing evaporation with boiling. Boiling happens at one temperature, throughout the liquid, with bubbles. Evaporation happens at any temperature, only at the surface.

4. 04

   Explaining evaporation's cooling effect without 'most energetic': the fastest particles escape, so the average kinetic energy of those remaining falls — and average kinetic energy is temperature.

One worked example, done properly