Microscopic interpretation of evaporation

  Fig. 1-16 Microscopic interpretation of evaporation. Particles with higher kinetic energy leave the surface of a liquid.

Inside a liquid, the distribution of kinetic energy of the particles is random and some has higher and some lower kinetic energies. The energetic particles have enough energy to overcome the attractive forces between them and leave the liquid through the liquid surface.

As the particles that leave the liquid are the high-energy particles, the average kinetic energy of the liquid particles decreases and thus the temperature of the liquid decreases. Thus the liquid cools down during evaporation. Since evaporation is a change of phase from liquid to gas, latent heat of vaporization is involved. In other words, the evaporated vapour takes away latent heat and cools down the liquid.