specific latent heat

• Internal energy


  The total kinetic energy and potential energy of the particles in an object
• Specific heat capacity


  The amount of energy needed to raise the temperature of 1 kg of substance by 1°C
• Specific latent heat


  The amount of energy needed to melt or vaporise 1 kg at its melting or boiling point
• Specific latent heat is the amount of energy required to change the state of 1 kilogram (kg) of a material without changing its temperature
• Types of specific latent heat

  • Latent heat of fusion - the amount of energy needed to melt or freeze the material at its melting point
  • Latent heat of vaporisation - the amount of energy needed to boil or condense the material at its boiling point
• Typical values for specific latent heat

  • Water: Latent heat of fusion 334 kJ/kg, Latent heat of vaporisation 2,260 kJ/kg
  • Lead: Latent heat of fusion 22.4 kJ/kg, Latent heat of vaporisation 855 kJ/kg
  • Oxygen: Latent heat of fusion 13.9 kJ/kg, Latent heat of vaporisation 213 kJ/kg
• An input of 334,000 joules (J) of energy is needed to change 1 kg of ice into 1 kg of water. The same amount of energy needs to be taken out of the liquid to freeze it
• Calculating thermal energy changes

  change in thermal energy = mass × specific latent heat
• Calculating energy needed to freeze 500 grams (g) of water from 0°C

  • Energy = 0.5 kg × 334,000 J/kg = 167,000 J
• Measuring latent heat


  1. Use a heating curve graph to identify the horizontal lines where energy is used for state change, not temperature increase

  2. The amount of energy represented by the horizontal lines is equal to the latent heat
• Calculating latent heat of vaporisation of water

  • If a 60 W heater provides 226,800 J over 63 minutes to 100 g of water, the latent heat of vaporisation is 2,268,000 J/kg