Matter in Our Surrounding Notes

• The quantity of heat required to convert one unit mass of a liquid into vapour at its boiling point without any change of temperature is called its latent heat of vapourisation.

Latent heat of vapourisation =

Latent heat of vapourisation of water:

• The latent heat of vapourisation of water is the amount of net required to convert one unit mass of water into vapour at its boiling point (i.e., at 100ºC at 1 atm pressure)

Latent heat of vapourisation of water = 22.6 × 10⁵ J/kg

• The process of a liquid changing into vapour (or gas) even below its boiling point is called evaporation.
• Amount of energy equal to the latent heat of vapourisation is absorbed by water during its transformation from liquid to gaseous state.

Factors Affecting Evaporation:

• The evaporation of a liquid depends mainly on the following factors:

1. Temperature

2. Surface area

3. Humidity

4. Wind speed