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Adhesion and Cohesion Difference - Definitions, Relationship, FAQs

Adhesion and Cohesion Difference - Definitions, Relationship, FAQs

Team Careers360Updated on 02 Jul 2025, 04:58 PM IST

In our daily lives, we see evidence of adhesiveness and cohesiveness in many facets of our lives. One of the common phenomena in adhesion and cohesion is force. Despite the fact that they have a similar sounding name, these things are commonly referred to by different names. The link between adhesion and cohesion can be described using surface tension, which is an important water property. As for the definitions, adhesion is the propensity of two or more molecules to form a chemical bond. As opposed to this, Cohesion refers to the force that draws similar molecules together.

This Story also Contains

  1. Cohesive forces
  2. Adhesive forces
  3. Relationship between cohesion and adhesion
  4. Difference between adhesion and cohesion:

Cohesive forces

Hydrogen bonds and van der Waals forces are examples of intermolecular forces that contribute to the bulk feature of liquids, which is their inability to separate. These attraction forces exist specifically between molecules of the same material. For example, rain falls in droplets rather than a fine mist because water has a high degree of cohesion, which binds the molecules of water together securely to create droplets. Due to the molecules' hatred of their environment, this force tends to bring liquid molecules together, resulting in huge clusters.

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Commonly Asked Questions

Q: What causes surface tension in liquids?
A:
Surface tension is caused by cohesive forces between liquid molecules at the surface. These molecules are pulled inward by other molecules deeper inside the liquid, creating a "skin-like" effect on the surface.
Q: Why do some insects can walk on water?
A:
Some insects can walk on water due to surface tension, which is a result of strong cohesive forces between water molecules. The insect's weight is distributed over a large area by its legs, allowing it to be supported by the "skin" created by surface tension.
Q: How do detergents reduce surface tension?
A:
Detergents reduce surface tension by weakening the cohesive forces between water molecules at the surface. They do this by inserting themselves between water molecules, disrupting the hydrogen bonding network.
Q: What is the role of cohesion in plant transpiration?
A:
Cohesion is crucial in plant transpiration. It allows water molecules to form continuous columns in the xylem, enabling water to be pulled up from the roots to the leaves against gravity. This phenomenon is known as cohesion-tension theory.
Q: What is the difference between adhesive and cohesive failure?
A:
Adhesive failure occurs when the bond between two different materials breaks at their interface. Cohesive failure happens when a material breaks within itself. For example, if glue separates from wood, it's adhesive failure; if the glue breaks internally, it's cohesive failure.

Adhesive forces

The force of attraction between different substances/objects is referred to as the term "adhesive forces". It includes mechanical forces (sticking together) and electrostatic forces (attraction due to opposing charges). Adhesion occurs when a liquid wetting agent adheres to the surface it is resting on. When water is spilled on a clean piece of glass, it spreads out and leaves behind a thin, even film on the surface. The reason for this is adhesive force. Water molecules are pulled out of the spherical shape due to the adhesive forces between water and glass and hold them against the glass's surface, as a result, the attraction between like molecules is avoided.

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Adhesive forces

Commonly Asked Questions

Q: What is adhesion in chemistry?
A:
Adhesion is the attraction between molecules of different substances. It's the force that causes water to stick to glass or paint to adhere to a wall. Adhesion occurs due to intermolecular forces between unlike molecules.
Q: How do adhesive forces affect the shape of liquid droplets on surfaces?
A:
Adhesive forces between a liquid and a surface influence the shape of droplets. Strong adhesion causes droplets to spread out and have a lower contact angle with the surface. Weak adhesion results in more spherical droplets with higher contact angles.
Q: Can you explain the concept of work of adhesion?
A:
The work of adhesion is the energy required to separate two different substances at their interface. It's a measure of the strength of adhesive forces between the substances. Higher work of adhesion indicates stronger adhesion between the materials.
Q: What is the relationship between adhesion and adsorption?
A:
Adhesion and adsorption are related concepts. Adsorption is a specific type of adhesion where molecules, atoms, or ions from a gas or liquid adhere to a solid surface. The strength of adhesive forces determines the extent of adsorption.
Q: How do adhesion and cohesion affect the process of distillation?
A:
In distillation, cohesion keeps the liquid molecules together as they vaporize and condense. Adhesion affects how the condensed liquid interacts with the condenser surface, influencing the efficiency of the process and the purity of the distillate.

Relationship between cohesion and adhesion

Cohesion and adhesion forces can be found in a variety of activities and processes. As an illustration, consider the meniscus, which is a Both adhesion and cohesion are to blame for liquid surface curvature when kept in a tube or container. In physics, adhesion is the force that pulls liquid against the container wall at its edges. Cohesion is created by the attraction force between water molecules, which causes the liquid's surface to bend in the middle.

The form of the meniscus is also determined by these forces. The meniscus will have a convex form if the adhesion force between the liquid and the inner tube surface is lesser than the cohesion force between the liquid molecules. As an illustration, consider mercury, which is housed in a transparent tube. Similarly, a concave meniscus will result if adhesion is greater than cohesion. For instance, water in a glass tube.

Surface will be parallel when adhesion and cohesion are the same. Assume you've just dropped some water on something. Unless the surface has a high adhesive force, water will run off and become soaked into the fabric. If the cohesive force is strong, water molecules will be more attracted to one another than surface molecules are to one another. As a result, water is absorbed at a slower rate on the surface of the water.

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The macroscopic effects of adhesive and cohesive forces

A liquid's form is defined by the strength of the cohesive and adhesive forces operating on it when it's applied to a smooth surface (and whether or not it will wet the surface).For a given liquid and surface combination, more adhesive forces cause the liquid to sink and saturate the surface beneath it; this is called evaporation. However, if the cohesive forces within the liquid are stronger, the liquid will be able to resist the adhesion and keep its spherical shape, causing it to bead on the surface.

Meniscus is the curvature of a liquid's surface inside a container, like a graduated cylinder.. Be that as it may, we must first understand the adhesive forces acting on surface tension in order to describe why some liquids have a concave up meniscus although others have a concave down meniscus. Water, for example, is a polar molecule with a partial positive charge and partial negative charge on the hydrogens and the oxygen respectively.

As a result, in liquid water, each molecule's partial positive charge attracts the adjacent molecule's partial negative charge. Cohesive forces in water originate here. Because the water molecules are being pulled and pushed equally in all directions, there is no net force on them. As a result, the molecules on the liquid's surface have a net downward pull because they lack upward pushing forces.

The solution lies in the interaction of water molecules' adhesive forces with the container's surface. Liquid convects downward to lessen contact with the wall's surface when its cohesive force is greater than its adhesive force on the wall. When the liquid's adhesive force to the wall exceeds its cohesive force, upward concavity is observed as the liquid is more attracted to the wall than its neighbors.

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Commonly Asked Questions

Q: Why do water droplets form on leaves?
A:
Water droplets form on leaves due to a combination of cohesion and adhesion. Cohesion causes water molecules to stick together, forming droplets, while adhesion allows these droplets to stick to the leaf surface.
Q: How does adhesion contribute to capillary action?
A:
Adhesion plays a crucial role in capillary action by causing liquids to climb up narrow spaces against gravity. The liquid molecules adhere to the walls of the capillary tube, pulling the liquid upward.
Q: Why does water form a dome-like shape on a penny?
A:
Water forms a dome-like shape on a penny due to cohesion and surface tension. The water molecules are strongly attracted to each other, allowing the water to be held together in a shape that exceeds the penny's edges, despite gravity pulling it down.
Q: How does adhesion affect the boiling point of liquids?
A:
Adhesion can affect boiling points indirectly. In a liquid with strong adhesive forces to its container, more energy is required to overcome these forces and form bubbles. This can slightly increase the observed boiling point compared to the same liquid in a container with weaker adhesion.
Q: How do adhesion and cohesion contribute to the water cycle?
A:
In the water cycle, cohesion keeps water droplets together in clouds and allows for surface tension in bodies of water. Adhesion helps water stick to soil particles and plant surfaces, aiding in processes like transpiration and soil moisture retention.

Difference between adhesion and cohesion:

These two terms refer to forces of attraction that exist between separate molecules and inside the same molecule. Despite the fact that they sound similar, they aren't the same.

  1. Adhesion occurs when two dissimilar molecules or substances come together and stick to one another. A cohesion force is generated when two comparable molecules or substances are attracted by the force of attraction.

  2. Water molecules are attracted to the xylem vessel walls because of adhesion. Within the water molecules, cohesion force is rampant.

  3. The adhesion effects include meniscus and capillary action, as well as (the curved liquid surface in a cylinder). Cohesion has effects on the meniscus, capillary action, and surface tension.

  4. Mechanical or electrical forces generate adhesion between two different substance types. Van der Waals forces and hydrogen bonding cause cohesion.

  5. The liquid can spread all over the surface due to any of the high adhesion forces that are in work there. Water droplets develop on any surface due to a strong cohesive force.

  6. Molecules are drawn to one another by electrostatic attraction. Molecules with similar properties tend to group together.

  7. A liquid's surface tension, water droplets, and capillary action are all caused by surface tension. It's because of the adhesion that a liquid like paint, glue, and cement spreads over a hard surface.

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NCERT Chemistry Notes:

Commonly Asked Questions

Q: How does cohesion differ from adhesion?
A:
Cohesion is the attraction between molecules of the same substance, while adhesion is between different substances. For example, water droplets form due to cohesion, but water sticking to a leaf is due to adhesion.
Q: Why does mercury not wet glass surfaces?
A:
Mercury doesn't wet glass surfaces because the cohesive forces between mercury atoms are stronger than the adhesive forces between mercury and glass. This results in mercury forming distinct droplets on glass rather than spreading out.
Q: What role does adhesion play in the formation of menisci?
A:
Adhesion is responsible for the curved surface (meniscus) formed by liquids in containers. When adhesive forces between the liquid and container are stronger than cohesive forces within the liquid, a concave meniscus forms (like water in glass). The opposite results in a convex meniscus (like mercury in glass).
Q: Can you explain the relationship between cohesion and surface tension?
A:
Cohesion is directly related to surface tension. Stronger cohesive forces between liquid molecules result in higher surface tension. This is why water, with its strong hydrogen bonds, has a higher surface tension than many other liquids.
Q: How does the concept of wetting relate to adhesion and cohesion?
A:
Wetting occurs when adhesive forces between a liquid and a solid are stronger than the cohesive forces within the liquid. This causes the liquid to spread out on the solid surface rather than beading up. The degree of wetting depends on the balance between adhesion and cohesion.

Frequently Asked Questions (FAQs)

Q: How do adhesion and cohesion contribute to the phenomenon of superhydrophobicity?
A:
Superhydrophobicity occurs when a surface is extremely water-repellent. It results from a combination of surface chemistry (low adhesion to water) and surface roughness. The low adhesion causes water to bead up, while the roughness traps air pockets, further reducing contact between water and the surface. Cohesion within the water droplets keeps them as nearly spherical beads on the surface.
Q: What is the significance of adhesion and cohesion in understanding capillary condensation?
A:
Capillary condensation occurs when vapor condenses in small pores at pressures below the saturated vapor pressure of the bulk liquid. This phenomenon depends on both the adhesion between the vapor and pore walls and the cohesion within the condensed liquid. The balance of these forces determines at what pressure condensation occurs in pores of different sizes.
Q: How do adhesion and cohesion affect the formation of raindrops?
A:
Cohesion causes water molecules in the atmosphere to stick together, forming tiny droplets. As these droplets collide, they coalesce due to surface tension (a result of cohesion). Adhesion to dust particles in the air can provide nucleation sites for droplet formation.
Q: How do temperature changes affect the balance between adhesion and cohesion?
A:
Temperature changes can alter the balance between adhesion and cohesion. Generally, as temperature increases, both adhesive and cohesive forces weaken due to increased molecular motion. However, the rate of change may differ, potentially shifting the balance between these forces and affecting phenomena like wetting and surface tension.
Q: What is the role of surfactants in modifying adhesion and cohesion?
A:
Surfactants modify the balance between adhesion and cohesion by reducing surface tension. They can increase wetting and spreading by reducing cohesion within a liquid, and can also modify adhesion between liquids and surfaces. This makes them crucial in processes like cleaning, emulsification, and dispersion.
Q: How do adhesion and cohesion affect the process of coating surfaces?
A:
In coating processes, adhesion between the coating material and the surface is crucial for durability and effectiveness. Cohesion within the coating material ensures it forms a continuous, uniform layer. The balance between these forces affects properties like thickness, coverage, and resistance to peeling or flaking.
Q: What is the difference between mechanical and chemical adhesion?
A:
Mechanical adhesion occurs when an adhesive hardens within the pores of a surface, creating a physical interlocking. Chemical adhesion involves the formation of chemical bonds (covalent, ionic, or hydrogen bonds) between the adhesive and the surface. Many practical adhesives rely on a combination of both types.
Q: How do adhesion and cohesion affect the properties of polymers?
A:
In polymers, cohesion between polymer chains determines properties like strength and elasticity. Adhesion between the polymer and other materials affects properties like wettability and the ability to form composites. The balance of these forces is crucial in determining the overall behavior of polymer materials.
Q: What is the role of adhesion in cell biology?
A:
In cell biology, adhesion is crucial for cell-cell and cell-matrix interactions. Cell adhesion molecules on cell surfaces allow cells to stick to each other and to the extracellular matrix, which is essential for tissue formation, wound healing, and many other biological processes.
Q: How do adhesion and cohesion affect the formation of stalactites and stalagmites?
A:
Adhesion allows water droplets to cling to cave ceilings, while cohesion keeps the droplets together. As the water evaporates, it leaves behind dissolved minerals. Over time, these minerals build up due to both adhesion to the existing formation and cohesion with each other, forming stalactites and stalagmites.
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