Difference Between Adsorption and Absorption

Edited By Team Careers360 | Updated on Jul 02, 2025 04:55 PM IST

What is absorption?

Absorption (absorption in Hindi is ‘avashoshan’) is a phenomenon (phenomenon Tamil meaning is ‘Nikaḻvu’) of assimilation (assimilation meaning in Tamil is ‘Oruṅkiṇaippu’) in which the constituent of a substance enters into bulk phase of another substance. In absorption, one substance is completely absorbed (absorb meaning in Tamil is ‘Uṟiñci’) in another substance. This is also a key difference between absorption and adsorption. Absorption may be of reactive nature or non-reactive nature. Chemical absorption is absorption of reactive nature.

This Story also Contains

What is absorption?
What is adsorption?
What is desorption and what is sorption?
Distinguish between adsorption and absorption.

In Chemical absorption or reactive absorption, a chemical reaction takes place between the absorbed (adsorbed meaning in Marathi is ‘Gaḍhūna gēlēlā’) and the absorbing (absorbing meaning in Hindi is ‘avashoshit’) substances. Chemical absorption depends upon the concentration of its reactants and stoichiometry of the reaction.

Physical absorption is absorption of non-reactive nature. A physical absorption or non-reactive absorption depends on the absorbing (absorbing meaning in Hindi is ‘avashoshit’) substance and absorbed (adsorbed meaning in Marathi is ‘Gaḍhūna gēlēlā’) substance. It also depends on physical properties such as temperature, solubility and pressure. The substance which is getting absorbed is called absorbate and absorbent is substance absorbing the absorbent (absorbent meaning in Tamil is ‘Uṟiñcum’). Example: a sponge soaking water, liquid absorbed by solid, biological absorption of digested food by the wall of the intestine, etc.

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What is adsorption?

Adsorption (adsorption in Hindi is called ‘adhishoshan’ and adsorption in Tamil is ’Uṟiñcutal’) is the phenomenon in which adhesion of constituents of a substance takes place on surface of another substance. This is the most important characteristic to spot difference between absorption and adsorption. The substance getting adsorbed is called adsorbate (adsorbate meaning in Tamil is ‘parappirppi’) while the substance on which adsorbate is adsorbing is called adsorbent (adsorbent meaning in Tamil is ‘Uṟiñcum’). This is the key difference between adsorbent and adsorbate. Examples of adsorbent include alumina gel, zeolites, activated carbon, graphite, silica gel etc.

The process of adsorption takes place due to the condition that forces acting on the particles present on the surface of a substance are uneven. This is very distinct to forces acting on the bulk particles of the material. Unlike the particles inside the bulk, the particles present on the surface exposed to the environment are not surrounded by other constituents from all sides. The forces on the inside of the bulk phase balance each other whereas those on the exposed surface of the substance are unbalanced.

These unbalanced residual forces present on the surface attract the adsorbate particles by the process of adsorption. The difference between absorption and adsorption originates because of the fact that absorption is bulk phenomenon while adsorption is surface phenomenon. The greater is the surface area of adsorbent, higher is the extent of adsorption at a given temperature and pressure. Adsorption is dependent on temperature. Example: pollution mask, charcoal gas mask, etc. After understanding the definition of absorption and adsorption, we can now easily pinpoint the difference between absorption and adsorption.

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What is desorption and what is sorption?

Desorption (desorption meaning in Hindi is ‘vishoshan’) is the phenomenon in which the constituents of a substance detaches or removes itself from a surface or bulk matter. Sorption (sorption meaning in Hindi is ‘shoshan’) is the process of accumulation of constituents of one substance into another substance. The act of attachment in sorption and detachment in desorption highlights the main difference between desorption and sorption.(It is important to understand desorption and sorption to recognize the difference between absorption and adsorption. This is because all the processes are quite similar superficially but differ conceptually.)

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Distinguish between adsorption and absorption.

To differentiate between adsorption and absorption (‘avashoshan’ is the Hindi meaning of absorption) we need to first understand the difference between absorb and adsorb (meaning of adsorb in Hindi is ‘sokh lena’). Absorb meaning is to assimilate one substance into another while adsorb means to assimilate on a surface.

Difference between absorption and adsorption is given in the following table

Absorption	Adsorption
It is a phenomenon of assimilation in which the constituent of a substance enters into the bulk phase of another substance.	It is the phenomenon in which adhesion of constituents of a substance takes place on the surface of another substance.
It is a bulk phenomenon	It is surface phenomenon
The constituent of absorbate spread uniformly throughout the absorbent.	The constituents of adsorbate concentrate only on the surface of adsorbent.
It is endothermic process	It is exothermic process
It remains unaffected by temperature	It is a temperature dependent phenomenon.
The rate of reaction is uniform for absorption	The rate of reaction increases slowly and then achieves equilibrium.
Absorption examples include the absorption of liquid by a sponge.	Examples include adsorption of pollutants by pollution marks.

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Frequently Asked Questions (FAQs)

1. Write the absorption definition. Give an example for absorption.

Absorption (absorption Hindi meaning is ‘avashoshan’) is a phenomenon (phenomenon Tamil meaning is ‘Nikaḻvu’) of assimilation (assimilation meaning in Tamil is ‘Oruṅkiṇaippu’) in which the constituent of a substance enters into bulk phase of another substance. In absorption, one substance is completely absorbed (absorb meaning in Tamil is ‘Uṟiñci’) in another substance. Example: a sponge soaking water, liquid absorbed by solid etc.

2. Define absorb.

Absorb meaning is to assimilate one substance into another while adsorb means to assimilate on a surface.

3. Define desorption.

Desorption (desorption meaning in Hindi is ‘vishoshan’) is the phenomenon in which the constituents of a substance detaches or removes itself from a surface or bulk matter.

4. What is the difference between adsorption and absorption?

The difference between absorption and adsorption is:

Absorption	Adsorption
It is a phenomenon of assimilation in which the constituent of a substance enters into the bulk phase of another substance.	It is the phenomenon in which adhesion of constituents of a substance takes place on the surface of another substance.
It is a bulk phenomenon	It is surface phenomenon
The constituent of absorbate spread uniformly throughout the absorbent.	The constituents of adsorbate concentrate only on the surface of adsorbent.
It is endothermic process	It is exothermic process
It remains unaffected by temperature	It is a temperature dependent phenomenon.
The rate of reaction is uniform for absorption	The rate of reaction increases slowly and then achieves equilibrium.
Examples include absorption of liquid by a sponge.	Examples include adsorption of pollutants by pollution marks.

5. Define absorbent.

Absorbent is an insoluble substance that is covered by liquid on its surface.

6. What is the fundamental difference between adsorption and absorption?

Adsorption is a surface phenomenon where molecules or atoms adhere to the surface of a material, while absorption involves the entire bulk of the material taking in substances. In adsorption, particles stick to the surface; in absorption, they penetrate into the material.

7. How does the process of absorption differ from adsorption?

Absorption involves the uptake of a substance (absorbate) into the entire volume of the absorbing material (absorbent). The absorbed substance distributes throughout the bulk of the material, unlike in adsorption where it remains on the surface.

8. How does absorption differ from adsorption in terms of the final location of the absorbed/adsorbed substance?

In absorption, the absorbed substance is distributed throughout the entire volume of the absorbing material. In contrast, during adsorption, the adsorbed substance remains on the surface of the adsorbent material, forming a thin layer or film.

9. What is the role of surface area in adsorption?

Surface area plays a crucial role in adsorption. The greater the surface area of the adsorbent, the more sites are available for adsorption to occur. This is why many adsorbents, like activated charcoal, are designed to have a highly porous structure, maximizing their surface area and adsorption capacity.

10. How does temperature affect adsorption and absorption processes?

Temperature generally has opposite effects on adsorption and absorption. Adsorption is typically an exothermic process, so increasing temperature usually decreases adsorption. Absorption, on the other hand, is often endothermic, so higher temperatures can increase the rate of absorption.

11. What is the difference between physical absorption and chemical absorption?

Physical absorption involves the dissolution of a substance into a liquid or solid without chemical bonding. Chemical absorption, or chemisorption, involves chemical reactions between the absorbed substance and the absorbent. Physical absorption is generally reversible and has lower absorption energies compared to chemical absorption.

12. How does absorption differ from adsorption in terms of energy changes?

Adsorption is typically exothermic (releases heat) because molecules lose energy as they adhere to the surface. Absorption, however, can be either exothermic or endothermic, depending on the specific system. The energy change in absorption often involves breaking and forming bonds as the absorbed substance integrates into the bulk material.

13. Why is adsorption often confused with absorption?

Adsorption and absorption are often confused because both processes involve the uptake of one substance by another. The key difference lies in where the uptake occurs - on the surface (adsorption) or throughout the volume (absorption). The similar-sounding names and the fact that both processes can occur simultaneously in some systems contribute to the confusion.

14. How does adsorption differ from surface tension?

While both are surface phenomena, adsorption involves the accumulation of molecules on a surface, whereas surface tension is a property of a liquid's surface resulting from intermolecular forces. Adsorption can affect surface tension by changing the composition of the surface layer, but they are distinct concepts.

15. How does adsorption contribute to the purification of water?

Adsorption plays a crucial role in water purification by:

16. Why is adsorption considered a surface phenomenon?

Adsorption is considered a surface phenomenon because it occurs only on the surface of the adsorbent. The molecules or atoms (adsorbate) attach to the surface without entering the bulk of the material, resulting in a higher concentration of the adsorbate on the surface compared to the surrounding medium.

17. Can you explain the concept of 'adsorbate' and 'adsorbent'?

In adsorption, the 'adsorbate' is the substance being adsorbed (usually a gas or liquid), while the 'adsorbent' is the material onto whose surface the adsorption occurs (usually a solid). For example, in activated charcoal filters, the impurities in water are the adsorbate, and the activated charcoal is the adsorbent.

18. What are some common examples of adsorption in everyday life?

Common examples of adsorption include:

19. What is meant by 'physisorption' in the context of adsorption?

Physisorption, or physical adsorption, refers to adsorption where the adsorbate adheres to the surface through weak intermolecular forces like van der Waals forces. It doesn't involve the formation of chemical bonds and is generally reversible. An example is the adsorption of nitrogen gas on the surface of activated charcoal.

20. How does the size of adsorbate molecules affect the adsorption process?

The size of adsorbate molecules influences adsorption in several ways:

21. What is desorption, and how is it related to adsorption?

Desorption is the reverse process of adsorption, where adsorbed molecules leave the surface of the adsorbent. It's closely related to adsorption as both processes occur simultaneously, reaching an equilibrium. Understanding desorption is crucial for regenerating adsorbents and for applications like gas storage and separation.

22. Can you explain the concept of 'adsorption equilibrium'?

Adsorption equilibrium is the state reached when the rate of adsorption equals the rate of desorption. At this point, the amount of adsorbate on the surface remains constant over time. The equilibrium depends on factors like temperature, pressure, and the nature of the adsorbent and adsorbate.

23. How does pressure affect the adsorption of gases?

Generally, increasing pressure increases the adsorption of gases. As pressure increases, more gas molecules come into contact with the adsorbent surface, increasing the likelihood of adsorption. This relationship is often described by adsorption isotherms, such as the Langmuir isotherm or Freundlich isotherm.

24. What is meant by 'multilayer adsorption'?

Multilayer adsorption occurs when adsorbed molecules form multiple layers on the adsorbent surface, rather than just a single layer. This happens when the adsorbate-adsorbate interactions are stronger than the adsorbate-adsorbent interactions. The BET (Brunauer-Emmett-Teller) isotherm model is often used to describe multilayer adsorption.

25. What role does adsorption play in heterogeneous catalysis?

Adsorption is crucial in heterogeneous catalysis because:

26. How does 'chemisorption' differ from 'physisorption'?

Chemisorption, or chemical adsorption, involves the formation of chemical bonds between the adsorbate and the adsorbent surface. Unlike physisorption, chemisorption is often irreversible and involves higher energies. An example is the adsorption of oxygen on tungsten, forming tungsten oxide on the surface.

27. What is meant by 'adsorption isotherm'?

An adsorption isotherm is a curve describing the relationship between the amount of adsorbate adsorbed on the surface of an adsorbent and the equilibrium pressure or concentration of the adsorbate at a constant temperature. It helps characterize the adsorption process and the nature of the adsorbent-adsorbate interaction.

28. How does the polarity of adsorbate and adsorbent affect adsorption?

The polarity of both adsorbate and adsorbent significantly influences adsorption:

29. What is the difference between positive and negative adsorption?

Positive adsorption occurs when the concentration of adsorbate at the surface is greater than in the bulk solution. Negative adsorption, or depletion, happens when the concentration at the surface is less than in the bulk. Negative adsorption is less common and typically occurs with large molecules or particles that are excluded from the surface region.

30. How does the concept of 'adsorption capacity' relate to adsorbent effectiveness?

Adsorption capacity refers to the maximum amount of adsorbate that can be adsorbed by a given amount of adsorbent under specific conditions. It's a crucial measure of adsorbent effectiveness, indicating how much of a substance can be removed or stored. Higher adsorption capacity generally means a more effective adsorbent for a particular application.

31. What is the significance of the Langmuir adsorption isotherm?

The Langmuir adsorption isotherm is a model that describes monolayer adsorption on an ideal surface. It assumes:

32. How does the concept of 'specific surface area' relate to adsorption?

Specific surface area is the total surface area per unit mass of a material. It's crucial in adsorption because a higher specific surface area provides more sites for adsorption to occur. Materials with high specific surface areas, like activated carbon or zeolites, are often excellent adsorbents due to their numerous adsorption sites.

33. What is meant by 'selective adsorption', and why is it important?

Selective adsorption refers to the preferential adsorption of certain molecules or ions over others by an adsorbent. It's important because it allows for:

34. How does the shape of adsorbent particles affect the adsorption process?

The shape of adsorbent particles influences adsorption by:

35. What is the role of van der Waals forces in physisorption?

Van der Waals forces play a crucial role in physisorption:

36. How does the concept of 'breakthrough curve' relate to adsorption processes?

A breakthrough curve shows the concentration of adsorbate in the effluent of a fixed-bed adsorber over time. It's important because:

37. What is the difference between reversible and irreversible adsorption?

Reversible adsorption occurs when adsorbed molecules can be easily removed from the surface by changing conditions (e.g., temperature, pressure). Irreversible adsorption involves stronger interactions, often chemical bonds, making it difficult or impossible to remove the adsorbate without significantly altering the adsorbent. Physisorption is typically reversible, while chemisorption is often irreversible.

38. How does the porosity of an adsorbent affect its adsorption properties?

Porosity significantly influences adsorption properties:

39. What is the significance of the Freundlich adsorption isotherm?

The Freundlich isotherm is an empirical model describing non-ideal, reversible adsorption. Its significance lies in:

40. How does adsorption differ from ion exchange?

While both involve the uptake of substances from a fluid, they differ in:

41. What is meant by 'adsorption hysteresis', and why does it occur?

Adsorption hysteresis refers to the phenomenon where the adsorption and desorption isotherms do not coincide. It occurs because:

42. How does the concept of 'adsorption enthalpy' relate to the strength of adsorption?

Adsorption enthalpy is the heat released during adsorption. It relates to adsorption strength because:

43. What is the role of diffusion in adsorption processes?

Diffusion plays a crucial role in adsorption: