Specific latent heat of vaporization – revision notes

Latent heat is needed to change a liquid into a vapour (during vaporization). Let’s discuss on Specific latent heat of vaporization in detail.

role of latent heat of vaporization

If liquid molecules are to overcome the forces holding them together and gain the freedom to move around independently as gas molecules, they need a large amount of energy. They receive this as latent heat of vaporisation which increases the potential energy of the molecules but not their kinetic energy.

It also gives the molecules the energy required to push back the surrounding atmosphere in the large expansion that occurs when a liquid vaporises.


When the vaporization process is on, the temperature of the liquid remains constant.

The reading of a thermometer placed in water that is boiling remains constant at 100 ºC even though heat, called the latent heat of vaporisation, is still being absorbed by the water from whatever is heating it. When steam condenses to form water, latent heat is given out.


The specific latent heat of vaporisation (lv) of a substance is the quantity of heat needed to change unit mass from the liquid to vapour without a change of temperature.


Unit of specific latent heat of vaporization: The specific latent heat of vaporization is measured in J/kg or J/g.


In general, the quantity of heat Q to change a mass m from liquid to vapour is given by
Q = m × lv

Specific latent heat of vaporization – revision notes
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