13.2 Latent Heat of Fusion, Freezing, Vaporization and Condensation
During changes of state - from solid to liquid and vice versa or from liquid to vapor and vice
versa the temperature remains constant but the heat energy is required to be exchanged. The amount
of heat energy exchanged per unit mass of a substance is called Latent Heat.
Latent Heat of Fusion or Liquefaction
The amount of heat required per unit mass of a substance at melting point (constant) and under
1 Atmosphere pressure to convert it from the solid to the liquid state is called Latent Heat of Fusion.
Latent Heat of Freezing or Solidification
The amount of heat required per unit mass of a substance at freezing point (constant) and under
1 Atmosphere pressure to convert it from the liquid to the solid state is called Latent Heat of Freezing.
e.g. At 00C & 1 Atmosphere pressure 80 K-calorie of heat supplied to 1 Kg of ice melts it
into water and 80 K-Calorie of heat taken away from 1 Kg of water converts it into ice.
\ L = 80 Kcal / Kg = Latent heat of fusion of ice
Latent heat of freezing of water
Heat of Vaporization
The amount of heat required to vaporize a unit mass of liquid at its boiling point (constant)
and under 1 Atmosphere pressure it is called Latent Heat of Vaporization.
Latent Heat of Condensation
The amount of heat required to convert a unit mass of gas from its gaseous state into its liquid
state at its condensation point (constant) and under 1 Atmosphere pressure is called Latent Heat
e.g. 540 K-Cal of heat supplied under 1 Atmosphere to 1 Kg of water at
1000C converts it into steam conversely 540 K-Cal of heat taken away from steam at
1000C and 1 Atmosphere converts it into water.
\ L = Latent Heat of vaporization or condensation of water or steam
= 540 K-Cal / Kg.