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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