Question

Out of boiling and evaporation, which is a surface phenomenon? Explain.

Answer 1

Evaporation is a surface phenomena which results in cooling effect.
1.Evaporation can be defined as " The change of phase from liquid to gas that occurs at the surface of the liquid."
2. It is a cooling process because particles of liquid continuously give up their energy to the particles that are escaping from the surface.
Whereas Boiling is a Bulk phenomena where liquid will convert into gas at a constant temperature and constant pressure.

Example:
EVAPORATION OF SPIRIT UNDER FAN .
If air is blown over the liquid surface in an open pan. The number of molecules returned is reduced to a large extent . This is because any molecule escaping from the surface is blown away from the vicinity of the liquid.This increases it's rate of EVAPORATION.