Enthalpy of Vaporization of Water
Energy has to be added to liquid water to make it evaporate. This is the so-called enthalpy of vaporization, which can be calculated here. This energy input doesn't increase the temperature of the water (vapour).
H = [50,09-0,9298*T/1000-65,19*(T/1000)²] kj/mole Example: to evaporate one kilogram of water at a temperature of 20 degrees centigrade, an energy input of 2454 kilojoules is needed.
The energy for evaporation can be obtained from the environment; this creates evaporative cooling. For example, to completely evaporate one kilogram of water at 100 degrees Celsius, approximately 2257 kilojoules are required. This energy is extracted from the environment and leads to its cooling. By comparison, to heat one kilogram of water by one Kelvin, or degree Celsius, approximately 4.2 kilojoules are required, corresponding to the heat capacity of water.
Enthalpy is a term from thermodynamics. An old term for this quantity is heat content. Enthalpy thus roughly describes the heat energy inherent in a substance; this cannot be directly measured but can be calculated. In the case of the enthalpy of vaporization, it is the energy required to change the state of matter from liquid to gas, which is then contained in the water vapor. The enthalpy of vaporization is only a part of the total enthalpy of the water.