Latent heat of water

Latent heat              in Cal/g              J/kg

Of fusion                     80                  336 x 10³

Of vaporization          540               2256 x 10³

Sublimation: Sublimation is the process of conversion of a solid directly into vapour.

Sublimation takes place when boiling point is less than melting point.

Sublimation is shown by camphor or ice in vacuum.  

Hoar Frost: Hoar frost is just the reverse process of sublimation i.e. it is the process of direct conversion of vapour into solid.

Stream produces more severe burn than water at same temperature because internal energy of steam is more than that of water at same temperature.

Relative Humidity: Relative humidity is defined as the ratio of amount of water vapour present in a given volume of atmosphere to the amount of water vapour required to saturate the same volume at same temperature.

The ratio is multiplied by 100 to express the relative humidity in percentage.

Relative humidity is measured by Hygrometer.

Relative humidity increases with the increase of temperature. 

Air conditioning: For healthy and favourable atmosphere of human being, the conditions are as follows.

(i)                  Temperature : from 23˚ C to 25˚ C

(ii)                Relative humidity : from 60% to 65%

(iii)               Speed of air: from 0.75 meter / minute to 2.5 meter / minute.