Heat supplied or released by a substance for the change of phase is

`Q=mL` Where, L = latent heat.

`text{Latent Heat (L) :}`
The heat supplied to a substance which changes its state at constant temperature is called latent heat of the body. S.l. unit of latent heat 'L' is J/kg and C.G.S. unit is cal/gm.

`text(Latent Heat of Fusion)` (`L_f`) `:`
The heat supplied to a substance which changes it from solid to liquid state at its melting point and 1 atm pressure is called latent heat of fusion. Latent heat of fusion of ice is 80 cal/gm.

`text(Latent Heat of Vaporization)` (`L_v`) `:`
The heat supplied to substance which changes it from liquid to vapour state at its boiling point at 1 atm pressure is called latent heat of vaporization. Latent heat of vaporization of water is 540 cal/gm.

`text(Phase Change from ice at)` `0^oC` `text(to steam at)` `100^oC`

Suppose mass of ice is m gram. During state change from ice to water at `0^oC`, ice absorbed heat

`Q=mL_F`

After that temperature of water increases and water consumes heat `Q=msDeltaT` (where `DeltaT = 100^@C`).

Now water at `100^oC` converts into steam at `100^@C` and absorbed heat

`Q=mL_v`