Question

Difference between adhesion and cohesion

Answer 1

The rise or fall of a liquid in a capillary can be better understood by invoking the concepts of adhesion and cohesion.Cohesion means intermolecular attraction between like molecules in the liquid whereas adhesion means attraction between the liquid and the walls of the capillary.When adhesion is greater than cohesion,the liquid is said to wet the wall.This is what happens in the case of water and many other liquids.If cohesion is greater than adhesion,the liquid does not wet the wall.This is what happens in the case of mercury.Thus,when a drop of mercury or of water is put on a clean surface,the mercury drop becomes a truncated sphere since cohesion is greater than adhesion while the water drop spreads on the glass surface since adhesion is greater than cohesion.