Latent Heat of Fusion:

Fusion is the change of state from solid to liquid.  In the process of fusion, the molecule absorbs energy. This energy is latent heat. 

When a solid substance changes from the solid phase to the liquid phase, energy must be supplied in order to overcome the molecular attractions between the constituent particles of the solid. This energy must be supplied externally, normally as heat, and does not bring about a change in temperature.

The units of heat of fusion are usually expressed as joules per mole (the SI units) or calories per gram or Btu per pound-mole.

l (fusion) = 80 cal/gm or 334 KJ/Kg  

The specific latent heat of fusion is defined as

"The specific latent heat of fusion of a substance is the amount of heat required to convert unit mass of the solid into the liquid without a change in temperature."

 

The specific latent heat of fusion of ice at 0 ºC, for example, is 334 kJ.kg^-1. This means that to convert 1 kg of ice at 0 ºC to 1 kg of water at 0 ºC, 334 kJ of heat must be absorbed by the ice. Conversely, when 1 kg of water at 0 ºC freezes to give 1 kg of ice at 0 ºC, 334 kJ of heat will be released to the surroundings