Adhesion vs Cohesion: Difference and Comparison

Both the term Adhesion and Cohesion point towards the property of water. These terms help to understand the nature of water. Adhesion and Cohesion are attractive forces helping water molecules to make a bond with substances.

These forces come together but play different roles to give water its versatile nature.

Key Takeaways

1. Adhesion concerns the attraction between different types of molecules, whereas cohesion involves the attraction between similar molecules.
2. Adhesion leads to wetting and capillary action, while cohesion is responsible for surface tension and droplet formation.
3. Examples of adhesion include water sticking to the glass, while cohesion is evident in water’s spherical droplet shape.

Adhesion vs Cohesion

The difference between adhesion and cohesion is that adhesion is the force that acts between water and any other substance making it an intramolecular force. On the other hand, Cohesion is a force of attraction between two water molecules, making it an intermolecular force.

Adhesion is the reason behind water sticking to different surfaces. It also makes water spread over a surface when poured. Adhesion is related to an electrostatic force or mechanical force which is found to be strong.

This force gives the liquid it’s sticking property. Adhesion force needs to be sometimes stronger or sometimes even weaker, depending on the activity to be performed.

Cohesion is responsible for the spherical and clumpy structure of water. In other words, water molecules like hydrogen and oxygen are held by a cohesive force making water stable.

Cohesion is related to weak Van der Wall forces and surface tension. Cohesive force is the reason why we are able to store water in containers or else water molecules would not be attracted to each other.

Comparison Table

Parameter of Comparison	Adhesion	Cohesion
Definition	It exists between different types of molecules.	It exists between the same type of molecules.
Nature of Bond	Associated to an electrostatic force or mechanical force.	Associated to weak Van der walls forces and surface tension.
Type of Force	Intramolecular force	Intermolecular force
Results in	Gives water a spherical drop-like structure.	Makes water stick on various surfaces.
Example	Water droplets stick on the leaves of trees.	Water can be stored in the container.

What is Adhesion?

Adhesion is an attractive force helping substances to stick to one another. We can observe various activities in nature which prove the existence of adhesion.

During monsoons, one can notice water droplets sticking to the leaves of plants and trees. This force acts against the force of gravity and hence stops the water droplets from falling down.

The concave meniscus (curve on the surface of the water) exists due to the adhesive force acting between the glass tube and water molecules. However, it requires adhesion force to be stronger than cohesion force.

Adhesion also plays its role when it comes to capillary action, i.e. water moving in an upward direction.

Adhesion makes water molecules stick on the walls of plant vessels and helps water to move in an upward direction. We can also notice water molecules sticking on glass panels, cloth, paper, walls of the bottle, marble, and so many more substances due to adhesion.

The continuous flow of ink from the fountain pen tube to the paper is also possible due to adhesion. Hence it can be concluded that many of the day-to-day activities are supported by the force of adhesion.

What is Cohesion?

Cohesion can be referred to as unity. We know that unity binds people together. Similarly, cohesion is an attractive force which binds two molecules or substances together. Cohesion force sticks one water molecule to another. It helps to make the bond stable.  

Cohesion is an intrinsic property of a molecule that does not depend on external factors. The force is also responsible for surface tension. Cohesion, together with surface tension, gives water a spherical droplet-like structure.

Water hence occupies the least possible surface area when kept on a dry surface instead of being flat. In fact, cohesion is the reason behind rain falling down on the earth’s surface in the form of droplets.

Whenever we put the liquid from one container to another, we spill the liquid. It seems as if the liquid is sticking or moving towards the outside wall of the container from which we are pouring.

This could have easily been stopped if cohesive force was stronger than adhesive force. But the cohesive force between two water molecules is less strong than the adhesive force between a water molecule and the molecules of the container.

Main Differences Between Adhesion and Cohesion

1. Cohesion force exists between two similar molecules, whereas adhesion force exists between two different types of molecules.
2. Cohesion gives water a spherical structure, whereas adhesion gives it a sticky property. Hence both of these forces play their own specific roles.
3. In water, the force of adhesion is greater than the force of cohesion. Therefore water sticks to the wall of its container before falling down from the sides.
4. Adhesion force is present between water and plant vessels and is very important for the survival of plants. Cohesion is an internal property that helps liquid molecules to stick together.
5. Adhesion, if stronger than cohesion, gives a particular result and cohesion, if stronger than adhesion, reverses the initial result.

References

1. https://journals.sagepub.com/doi/abs/10.1177/104649640003100105
2. https://pubs.rsc.org/en/content/articlepdf/1948/df/df9480300162