Latent Heat of Vaporization

Evaporation is the change of state from liquid to vapor.  In the process of evaporation, the molecule absorbs energy. This energy is latent heat. 

How did you make the water evaporate?  Probably you added heat.  You might have set it out in the sun, or possibly put it over a fire.   To make water evaporate, you put energy into it. The individual molecules in the water absorb that energy, and get so energetic that they break the hydrogen bonds connecting them to other water molecules.  They become molecules of water vapor

l (vaporization) = 540 cal/gm or 2260 KJ/Kg 

The definition of the specific latent heat of vaporization is

'The specific latent heat of vaporization is the amount of heat required to convert unit mass of a liquid into the vapour without a change in temperature."

 

For water at its normal boiling point of 100 ºC, the latent specific latent heat of vaporization is 2260 kJ.kg^-1. This means that to convert 1 kg of water at 100 ºC to 1 kg of steam at 100 ºC, 2260 kJ of heat must be absorbed by the water. Conversely, when 1 kg of steam at 100 ºC condenses to give 1 kg of water at 100 ºC, 2260 kJ of heat will be released to the surroundings