Latent Heat (enthalpy) is the "hidden" heat when a substance absorbs or releases heat without producing a change in the temperature of the substance, eg, during a change of state.

Latent Heat of Fusion(

*)*

**L**_{f}Latent Heat (enthalpy) of Fusion is the heat absorbed per mole when a substance changes state from solid to liquid at constant temperature (melting point).

The unit for

*is Joule(J).*

**L**_{f}Specific Latent Heat of Fusion(l)

The specific latent heat is the amount of energy required to convert 1 kg (or 1 lb) of a substance from solid to liquid (or vice-versa) without a change in the temperature of the surroundings – all absorbed energy goes into the phase change.

Equation:

*=*

Q

Q

*m*l

where:

is the amount of energy released or absorbed during the change of phase of the substance (in kJ or in BTU),**Q**is the mass of the substance (in kg or in lb), and**m**is the specific latent heat for a particular substance (kJ/kg or in BTU/lb); substituted as**L**to represent as the specific latent heat of fusion**L**_{f}

Latent Heat of Vapourization(

*)*

**L**_{v}Latent Heat (enthalpy) of Vaporization (vaporisation) is the heat absorbed per mole when a substance changes state from liquid to gas at constant temperature (boiling point).

The unit for

**L**_{v }_{is Joule(J).Specific Latent Heat of Vapouriation(l)The amount of energy required to convert 1 kg (or 1 lb) of a substance from liquid to gas (or vice-versa) without a change in the external temperature is known as the specific latent heat of vaporization for that substance.Equation:}

_{ Q = mL }

_{}

where:

is the amount of energy released or absorbed during the change of phase of the substance (in kJ or in BTU),**Q**is the mass of the substance (in kg or in lb), and**m**is the specific latent heat for a particular substance (kJ/Kg or in BTU/lb); substituted as**L**as specific latent heat of vaporization.**L**_{v}

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