Changes of state and specific latent heat

• Internal energy


  The total kinetic energy and potential energy of the particles in an object
• Changing the internal energy of a material will cause it to change temperature or change state:

  • the energy required for a particular change in temperature is given by the specific heat capacity and the mass of material
  • the energy required for a particular change in state is given by the specific latent heat and the mass of material
• Specific latent heat


  the amount of energy needed to melt or vaporise 1 kg at its melting or boiling point
• latent heat of fusion


  the amount of energy needed to freeze or melt 1 kg of the material at its melting point
• latent heat of vaporisation


  the amount of energy needed to evaporate or condense 1 kg of the material at its boiling point
• Water

  • specific latent heat of fusion = 334kJ/kg
  • specific latent heat of vaporisation = 2260 kJ/kg
• Lead

  • specific latent heat of fusion = 22.4 kJ/kg
  • specific latent heat of vaporisation = 855 kJ/kg
• Oxygen

  • specific latent heat of fusion = 13.9kJ/kg
  • specific latent heat of vaporisation = 213kJ/kg
• The amount of thermal energy stored or released as the temperature of a system changes can be calculated using the equation:

  • energy required for a change of state = mass × specific latent heat
  • ΔE = m X l
• • energy is measured in joules (J)
  • mass is measured in kilograms (kg)
  • specific latent heat is measured in joules per kilogram (J/kg)
• Latent heat can be measured from a heating or cooling curve line graph