Specific heat capacity and latent heat

Different materials need different amounts of energy to warm up. Specific heat capacity is the energy to raise 1 kg by 1°C. Changing state takes energy too, without any change in temperature: that’s latent heat.

Key facts

  • Q = mcΔT.
  • Water’s specific heat capacity is about 4200 J/kg°C, which is very high.
  • Latent heat: Q = mL (no temperature change while melting or boiling).
  • Heating curves are flat during changes of state.

Worked examples

Example 1

How much energy heats 2 kg of water from 20°C to 100°C?

  1. ΔT = 80°C.
  2. 2 × 4200 × 80 = 672000 J

Answer: 672 000 J

Example 2

How much energy turns 0.5 kg of water at 100°C into steam? (L = 2.26 × 10⁶ J/kg)

  1. 0.5 × 2.26 × 10⁶ = 1.13 × 10⁶ J

Answer: 1 130 000 J