The latent heat of vaporisation of a water is the quantity of heat in joules required to convert 1 kilogram of the water (at its boiling point) to vapour or gas, without any change in temperature. The latent heat of vaporization of water is 22.5 × 10⁵ joules per kilogram (or 22.5 × 10⁵ j/kg). Hence it means that 22.5 × 10 5 J of heat is required to change 1 Kg of water (at its boiling point, 100°C) into steam at the same temperature of 100°C.