Latent heat of vaporization is the quantity of heat energy required to transform 1 kg of water at its boiling point 100 Celsius completely into gas is known as latent heat of vaporization. During boiling the temperature of water remains constant at 100 Celsius although heat is being constantly supplied to it. Thermometer therefore does not register any increase in temperature above 100 Celsius. All the additional heat energy supplied to the boiling water at 100 Celsius is utilized to transform the liquid state water into gaseous state.

The quantity of heat energy required to transform one kg of ice completely into water at 0 Celsius is known as latent heat of fusion. It is obvious that one kg of water at 0 Celsius is completely frozen into ice, same amount of heat will be given off from it. All solids require latent heat of fusion for melting. Latent heat of fusion can be easily understood from molecular theory of matter. When a solid is heated its molecules start vibrating more vigorously. As a result its temperature rises. If the solid continuous to absorbed heat, a point will be reached when the vibrations of molecules will reach to such an extent that they overcome the attraction which keeps the molecules bound together as a solid. At this point the solid starts melting.

The quantity of heat energy required to transform one kg of ice completely into water at 0 Celsius is known as latent heat of fusion. It is obvious that one kg of water at 0 Celsius is completely frozen into ice, same amount of heat will be given off from it. All solids require latent heat of fusion for melting. Latent heat of fusion can be easily understood from molecular theory of matter. When a solid is heated its molecules start vibrating more vigorously. As a result its temperature rises. If the solid continuous to absorbed heat, a point will be reached when the vibrations of molecules will reach to such an extent that they overcome the attraction which keeps the molecules bound together as a solid. At this point the solid starts melting.