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Latent heat


The energy needed to change the state of a substance from a solid to liquid or from a liquid to a gas heat energy is called LATENT HEAT energy. This energy is used not to heat up the substance but to separate the molecules from each other.

While a solid is melting and while a liquid is boiling there is no temperature change.

The amount of heat needed to change the state of 1 kg of a substance is called the SPECIFIC LATENT HEAT of the substance.

The units for specific latent heat are joules/kilogram (J/kg).

The specific latent heat of fusion is the heat needed to turn 1 kg of solid into a liquid at its melting point.
The specific latent heat of vaporisation is the heat needed to turn 1 kg of liquid into a gas at its boiling point.

Heat energy needed to melt or boil something = mass x specific latent heat
 
 
 
© Keith Gibbs 2008