Matter: Specific Latent Heat

Matter: Specific Latent Heat

Understanding Specific Latent Heat

  • The specific latent heat of a substance refers to the amount of energy needed to change the phase (state) of 1 kg of the substance without changing its temperature.
  • Energy changes during phase transitions are due to changes in the potential energy of the particles, not their kinetic energy.

Specific Latent Heat and Changes of State

  • There are two types of specific latent heat: latent heat of fusion and latent heat of vaporisation.
  • Latent heat of fusion is the energy required to change a substance from a solid to a liquid (melting) or vice versa (freezing) without a change in temperature.
  • Latent heat of vaporisation is the energy needed to change a substance from a liquid to a gas (evaporating, boiling) or vice versa (condensing) without change in temperature.

Calculating Specific Latent Heat

  • The formula used to calculate energy, mass, specific latent heat is E = m * L, where:
    • E = Energy transferred (Joules, J)
    • m = Mass of the substance (Kilograms, kg)
    • L = Specific latent heat (Joules per kilogram, J/kg)
  • This formula can be rearranged to find any one of the values if the other two are known.

Specific Latent Heat and Energy Conservation

  • During phase transitions, the conservation of energy principle still applies. As such, any energy that is absorbed or released due to a change of phase is balanced by a corresponding decrease or increase in the internal energy of the substance.
  • The energy supplied is not increasing the thermal (kinetic) energy of the particles but is being used to overcome intermolecular forces, hence the temperature does not change.