Which molecules – inside the liquid or on its surface – are involved in the evaporation process?

The evaporation process involves molecules only on the surface of the liquid. It is because of this that a puddle of a larger area with the same volume of liquid evaporates faster. Evaporation is a special case of the vaporization process – the transition of a substance from a liquid to a gaseous state. The process of vaporization throughout the entire volume of a liquid (i.e., with molecules inside the volume occupied by the liquid) is called boiling.

In the process of evaporation, the liquid leaves the molecules that are, first of all, on its surface.

It is “easier” for them to leave the mother environment, since the energy that is required for this is needed only to overcome the last barrier – the molecular bonds that hold the molecule in the “last layer” – on the water surface.

Molecules located deeper, in the water volume itself, will have to expend energy to break through first closer to the surface, and then into the last layer.

However, they will be able to “evaporate” in due time – as the “surface” molecules are removed, they will be replaced by molecules from the “nearest depth”, and molecules from the next “level of occurrence” will be pulled in place of these latter.