Difference Between Cohesion and Adhesion

Main Difference – Cohesion vs Adhesion

Adhesive and cohesive forces are forces of attraction. These forces explain the reason for the attraction or repulsion between different molecules. Adhesive forces describe the attraction between different molecules. Cohesive force describes the attraction between molecules of the same substance. Adhesion and cohesion are also very helpful in understanding some biological acts such as the water transportation through the xylem tube. Therefore, important facts about adhesion and cohesion along with their applications are discussed below in this article. The main difference between adhesion and cohesion is that cohesion is the property of molecules of the same substance to stick to each other whereas adhesion is the property of different molecules to stick to each other.

Key Areas Covered

1. What is Cohesion
      – Definition, Explanation with Examples
2. What is Adhesion
      – Definition, Explanation with Examples
3. What is the Relationship Between Cohesion and Adhesion
      – Cohesion and Adhesion
4. What is the Difference Between Cohesion and Adhesion
      – Comparison of Key Differences

Key Terms: Adhesion, Adhesive Force, Capillary Action, Cohesion, Cohesive Force, Meniscus, Xylem Tube

What is Cohesion

Cohesion is the attraction force between molecules of the same substance. It is a mutual attraction between molecules. This attraction force causes the molecules to stick together. Cohesive forces are intermolecular forces since these forces can be found between the molecules of the same substance.

These cohesion forces can be found in solid and liquid matter. The atoms or particles in solids and liquids are held together by these cohesive forces. Hydrogen bonding and Van Der Waal forces are types of cohesive forces.

A good example for the presence of cohesion forces can be found regarding water. The force attraction between water molecules is a type of cohesive force since it is a hydrogen bonding. A water droplet is formed due to this force. The effects of cohesion include surface tension, meniscus, and capillary action.

Figure 1: Formation of Water Droplets

The water molecules on the surface of the water are attracted by the water molecules in the middle of the water mass. This is the cohesion between water molecules. This causes the surface tension of water. The surface tension is the resistance to the rupture of the surface of the water. A meniscus is the curvature of the liquid surface within a container. The cohesion forces between liquid molecules cause this curvature. In capillary action, a liquid is drawn through a small tube against the gravity. Here, the cohesion between the liquid molecules helps the upward movement of the liquid.

What is Adhesion

Adhesion is the attraction force between molecules of different kinds. In other words, adhesion forces occur between different molecules. Adhesion can be defined as the preference to stick to other types of molecules.

Adhesion forces include electrostatic forces between two different molecules. For example, a strong adhesive force causes a liquid to spread over a solid surface. One of the major applications of adhesion in nature is the water transportation through xylem vessels. Here, the adhesion forces between the water molecules and the cell wall components help the water to move through xylem tube.

Figure 2: Meniscus in Mercury and Water

Capillary action and the meniscus are effects of adhesion. Capillary action is the movement of a liquid through a small tube against gravity. This occurs with the help of both adhesion and cohesion. The attraction force between liquid molecules and the tube wall is the adhesion here. In meniscus, the curvature of the liquid surface is helped by adhesion forces that act between the wall of the container and the liquid. The edges of the liquid are held by adhesion.

Relationship Between Cohesion and Adhesion

Cohesion and adhesion are related to each other. The two terms are used together to explain an effect. For example, the meniscus is caused by both adhesion and cohesion. Meniscus is the curvature of a liquid surface that is in a container. The edges of the liquid that is in touch with the wall of the container are held in an upper level with the help of adhesion forces. The middle of the liquid is curved due to the attraction force or the cohesion between the liquid molecules.

Difference Between Cohesion and Adhesion

Definition

Cohesion: Cohesion is the attraction force between molecules of the same substance.

Adhesion: Adhesion is the attraction force between different molecules.

Type of Attraction

Cohesion: Cohesion is an intermolecular attraction.

Adhesion: Adhesion is an intramolecular attraction.

Attraction Forces

Cohesion: Cohesion includes Van Der Waal forces and hydrogen bonding.

Adhesion: Adhesion includes electrostatic attractions.

Examples

Cohesion: Cohesion is the cause for the formation of water droplets on the surface tension of a liquid.

Adhesion: Adhesion is the cause for the spreading of a liquid on a solid surface.

Conclusion

Adhesion and cohesion are two types of attraction forces that occur between molecules. These forces act on a substance at the same time. Therefore the effects that arise from these forces are caused by both adhesion and cohesion. The main difference between cohesion and adhesion is that cohesion is the attraction force between molecules of the same substance whereas adhesion is the attraction force between molecules of different substances.

References:

1. “Cohesion.” Encyclopædia Britannica, Encyclopædia Britannica, inc., 23 Nov. 2011, Available here. Accessed 21 Sept. 2017.
2. “Cohesion and adhesion of water (Article).” Khan Academy, Available here. Accessed 21 Sept. 2017.
3. Libretexts. “Cohesive and Adhesive Forces.” Chemistry LibreTexts, Libretexts, 28 Aug. 2017, Available here. Accessed 21 Sept. 2017.

Image Courtesy:

1. “540604” (CC0) via PEXELS
2. “IMG_1658” by karabekirus (CC BY-SA 2.0) via Flickr