## Sunday, November 21, 2010

### Latent Heat

Latent Heat

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(Lf)

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 Lf is Joule(J).

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
= m
l

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

Latent Heat of Vapourization(Lv)

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 Lv 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:

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