Adhesion And Cohesion

There are a number of phenomena that explains various things which we observe in our everyday life. Although, we sometimes miss to focus onto these little things, and these help us to keep life going on earth. Adhesion and cohesion forces are one of the two phenomena. Though they sound to be similar, they are known to occur completely as different terms. Surface tension is one of the essential physical properties of water that describes the relationship between the adhesion and cohesion.

As for the definitions, the tendency of two or more different molecules to bond with each other is known as Adhesion, whereas the force of attraction between the same molecules is known as Cohesion.

The adhesion forces can be one of the results of electrostatic forces which are exerted on different substances. The cohesive forces are associated with Van der Waals forces and hydrogen bonding that cause liquids such as water to withstand the separation. When a glass surface is poured with water, both adhesive and the cohesive forces act on the surface of water. A strong adhesive force tends the liquid to spread over the surface whereas a strong cohesive force is responsible for the formation of water droplets on the water surface.

The adhesion and cohesion forces, both vary in their strengths. For example, if cohesion forces between the water molecules is strong than that of the adhesion forces between them, then the individual molecules will attract towards each other thus resulting to settling. In case, the adhesion forces of the water surfaces are strong than the that of the cohesion forces of the water molecules, then the water tends to disperse.

Differences Between Adhesion and Cohesion

Sr.no

Adhesion

Cohesion

1.

Adhesion happens between two dissimilar molecules or substances.

When two similar substances or molecules face force of attraction this force is known as cohesion force.

2.

Adhesion is generally the force of attraction present between the water molecules and the walls of xylem vessels.

Cohesion force is rampant among water molecules.

3.

Capillary action and meniscus (the curved surface which is formed by any liquid in a cylinder) are the effects of adhesion.

Surface tension, meniscus and capillary action are the effects of cohesion.

4.

Adhesion is caused by electrostatic or mechanical forces that exists among two kinds of different substances.

Cohesion is caused by hydrogen bonding and Van der Waals forces.

5.

A strong adhesion force causes the liquid to spread all over the surface.

A strong force of cohesion forms water droplets on any surface.


Practise This Question

The kinetic energy of an electron in the second Bohr orbit of a hydrogen atom is [a0 is Bohr radius]