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

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 of Condensation.

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

Index

13.1 Heat Capacity, Water Equivalent & Specific Heat
13.2 Latent Heat of Fusion, Freezing, Vaporization and Condensation
13.3 Mechanical Equivalent of Heat

Chapter 14