Question

In capillary action, why is the adhesive force of water to glass greater than the cohesive force of water to itself? Doesn't water have for hydrogen bonding?

Answer 1

Cohesive forces are the intermolecular forces arises from hydrogen bonding and Van der Waals forces which cause a tendency in liquids to resist separation. These forces exist between molecules of the same substance. This force tends to unite molecules of a liquid, gathering them into relatively large clusters due to the molecules' dislike for its surrounding. Adhesive forces are the attractive forces between unlike molecules which are caused as a result of mechanical forces (sticking together) and electrostatic forces (attraction due to opposing charges). In capillary action. when water is poured on clean glass, it tends to spread, forming a thin, uniform film over the glasses surface. This is because the adhesive forces between water and glass are strong enough to pull the water molecules out of their spherical formation and hold them against the surface of the glass, thus avoiding the repulsion between like molecules.