The Smarter Earth Institute

Heat of Vaporization of Water

Heat of Vaporization-the amount of heat required to convert unit mass of a liquid into the vapor without a change in temperature.

For water at its normal boiling point of 100 ºC, the  heat of vaporization is 2260 J g^-1. This means that to convert 1 g of water at 100 ºC to 1 g of  steam at 100 ºC,

2260 J of heat must be absorbed by the water. Conversely, when 1 g of steam at 100 ºC condenses to give 1 g of water at 100 ºC, 2260 J of heat will be released to the surroundings.

Heat of Vaporization of Water H_v = 2260 J /g

q= m H_v

The diagram on the left shows the uptake of heat by 1 kg of water, as it passes from ice at -50 ºC  to steam at temperatures above 100 ºC, affects the temperature of the sample. A: Rise in temperature as ice absorbs heat. B: Absorption of latent heat of fusion. C: Rise in temperature as liquid water absorbs heat. D: Water boils and absorbs latent heat of vaporization. E: Steam absorbs heat and thus increases its temperature. from-http://www.physchem.co.za/Heat/Latent.htm