Adhesion and Cohesion are the two classifications of the force of attraction that exist between molecules. People generally consider the two same as these two forces exist together however, the two are quite different from each other. The significant difference between Adhesion and Cohesion is that adhesion is an attractive force that exists between different types of molecules whereas cohesion is the attractive force existing between molecules of a similar type.
Surface tension is known to be an important physical property of water that provides a relationship between adhesion and cohesion. Both adhesion and cohesion are the results of Coulomb forces.
What is Surface Tension?
The molecules of water exhibit cohesive nature in general and thus liquid exhibits the property where a liquid surface resists an external force. This is known as Surface Tension. It is denoted by γ and its unit is dynes per centimeter.
For surface tension, it is said that this shows dependency on the force of attraction that exists between the water molecules along with the gaseous, liquid, or solid material in contact with it.
It is to be noted here that within a drop, all the molecules are surrounded by other molecules through equal force of attraction. This means that if some molecules are displaced away from the surface then the other water molecules will also exhibit attraction towards displacing molecules.
Content: Adhesion Vs Cohesion
Comparison chart
| Basis for Comparison | Adhesion | Cohesion |
|---|---|---|
| Basic | This exists between different molecules. | This exists between similar molecules. |
| Type of Attraction | Intramolecular | Intermolecular |
| Forms | Compounds (Paint, Glue) | Elements (Water droplet) |
| Type of force | Electrostatic force | Van der Waal forces |
| Behaviour | It causes liquid to get spread all over the surface. | Force that forms water droplets on any surface. |
Definition of Adhesion
Adhesion is defined as the force of attraction that exists between molecules of dissimilar substances. More simply, it is the attraction of one molecule for another type of molecule. It is a type of intramolecular force of attraction. Generally adhesive is the word which is used interchangeably for cement, glue, paste, etc. The reason for this is that adhesive is used to represent the bond.
Adhesives possess crucial physical as well as chemical properties. The three major factors associated with adhesion are adhesive, adherend, and surface.
When an adhesive bond is formed between molecules then there is a transitional zone that appears between adhesive and adherend. This zone is called interface and this region possesses somewhat different properties than the non-contact regions.
It is to be noted here that the stickiness of the substance exists due to intimate intermolecular contact.
One of the best examples of adhesion is a water droplet on a leaf or particles of water on the surface of a recently washed container.
Definition of Cohesion
The word cohesion is defined as the force of attraction existing between similar molecules. More simply, we can say, cohesion (which is an intrinsic property of any molecule) allows the body to remain concentrated throughout the mass as all the molecules are the same. It is sometimes known as cohesive attraction or cohesive force.
The strength which any cohesive substance possesses depends on the shape and structure of the molecules that have constituted it. Thus, we can say, cohesion is associated with the internal strength of the material.
It is to be noted here that molecules of any substance that get attracted to molecules of another substance do not exhibit cohesion.
One of the best examples of cohesion is the stickiness of various water molecules.
Key Difference Between Adhesion and Cohesion
- The key factor that differentiates adhesion from cohesion is that adhesion is the force of attraction that primarily exists between molecules that are dissimilar to each other while cohesion is the attractive force existing between similar molecules.
- As adhesion is the result of a combination of different molecules thus it results in the formation of compounds while cohesion is the result of a combination of the same molecules thus it forms elements.
- Due to the presence of different molecules, the intramolecular force of attraction exists in adhesion. However, because the same molecules are involved, therefore, the intermolecular force of attraction exists in the case of cohesion.
- The property of adhesion makes water attract water while due to the property of cohesion water is attracted to other entities.
- In adhesion, there exists hydrogen bond and weak van der Waals type of force whereas in cohesion there will be an electrostatic force.
- One of the finest examples of adhesion is sticking water droplets to the walls of the container while that of cohesion is the formation of water droplets.
Conclusion
Thus, this discussion concludes that adhesion and cohesion are the two mechanisms that are mainly associated with water and exist together. Adhesion and cohesion combinedly give rise to capillary action.