Question
Explain why cooling is caused after evaporation on the basis of kinetic theory?
Solution
According to the kinetic theory, the molecules of a liquid are moving with different velocities. The r.m.s velocity of the molecules is determined by the temperature of the liquid. Further, due to the intermolecular force of attraction acting downwards in the molecules, they do not leave the surface film of the liquid. But molecules having high velocity are able to overcome the force of attraction and hence escape. Therefore, the r.m.s velocity of the molecules which did not escape decreases and hence the temperature. So, cooling is followed by evaporation.
