Latent heat means the heat absorbed or released when substance changes its phase at constant temperature.
For example ice absorbs heat and converts into water but this does not change its temperature. when ice melts into water, its temperature is 0°C (latent heat of fusion) and temperature of water formed is also at 0 °C.
Latent heat of fusion
The latent heat of fusion of a solid substance is the quantity of heat required to change a solid substance into a liquid.
When ice melts to water the associated latent heat is known as latent heat of fusion. Latent heat of fusion is also associated when water freezes into ice.
Latent heat of vaporization
The heat associated with vaporizing a liquid or condensing vapour is known as latent heat of vaporization.
It is the amount of heat required to change the liquid to gas at a constant temperature. This differs for different liquids.
During boiling of water temperature of water remains at 100 °C till complete water gets evaporated. This all heat is absorbed by water as latent heat of vaporization.
What is latent heat?
The word latent is derived from Latin word “latere\” means to cover up. Thus the latent heat is extra heat provided to change the state of substance. For converting an ice cube into liquid at its melting point, latent heat is extra heat provided. For converting liquid to gas at its boiling point, latent heat is extra heat provided.
When phase of substance changes, its temperature does not changes but only molecular arrangement changes. Therefore latent heat means no change in temperature but only change of state.