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Types of latent heat

The latent heat of a substance depends on the change of state in question (e.g. solid to liquid).

  • The latent heat of fusion ($$L_{\text{f}}$$) is the heat required to change the state of a substance from solid to liquid at constant temperature.

    This is exactly equal to the heat released when the substance changes from a liquid to a solid.

  • The latent heat of vaporisation ($$L_{\text{v}}$$) is the heat required to change the state of a substance from liquid to gas at constant temperature.

    This is exactly equal to the heat released when the substance changes from a gas to a liquid.

These latent heat values have corresponding specific latent heat values ($$\ell_{\text{f}}$$ and $$\ell_{\text{v}}$$).

The specific latent heat of fusion of water is $$\ell_{\text{f}}=334 \text{ kJ}/\text{kg}$$ and the specific latent heat of vaporisation of water is $$\ell_{\text{v}}=2260 \text{ kJ}/\text{kg} $$.

The latent heat of fusion is the energy absorbed by ice when it melts into water
The latent heat of fusion is the energy absorbed by ice when it melts into water