Question

No heat is supplied to a liquid during evaporation. How does then the liquid change into its vapours?

Answer 1

Due to the weak intermolecular force of attraction, the molecules of a liquid move freely inside it. In the process, they collide with each other transferring energy between them. Molecules with higher kinetic energy reach the surface of the liquid. These molecules absorb some more heat from the surroundings to gain sufficient kinetic energy to overcome the force of attraction on them due to other molecules inside the liquid escaping from the surface into space. These escaping molecules form the vapour of the liquid. Thus, evaporation of the liquid happens even though no heat is supplied to it.