What Is The Difference between Absorption and Adsorption?

So, what is the main difference between absorption and adsorption? The former is the distribution of certain substances throughout the volume of another substrate while the latter is the attachment of a certain substance onto the surface of another substrate.

Chemistry is a branch of science that deals with the study of matter with its properties. It also describes how two substances combine with another substance with unique chemical properties. 

Besides that, it provides further descriptions on how to separate substances to give rise to a third substance. But all these chemical activities are possible due to intermolecular forces.  Intermolecular forces are responsible for attraction attributes between the same and different atoms or ions or molecules. The formation of a new substance occurs due to the attraction or repulsion of these atoms or molecules. 

Examples of intermolecular forces are ion bonding, hydrogen bonding, and Van Der Waals Forces. These forces result in physical differences between similar molecules in terms of boiling and melting points.  This article provides an explanation of the mechanism of adsorption and further differences between absorption and adsorption in a tabular form. Take time to read through and get to know the physical adsorption mechanism. 

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Difference between Absorption and Adsorption (With Table)

Basic Terms Absorption Adsorption
Meaning Assimilation of ions, atoms, or molecules into the bulk of the solid or liquid phase Accumulation of ions, atoms, or molecules on the surface of the bulk of solid or liquid
Occurrence A bulk phenomenon A surface bulk phenomenon.
Heat Exchange Endothermic Process Exothermic process
Temperature Not affected by temperatures. Work well under low temperatures.
Concentration Constant throughout the medium Prone to changes in the bulk of absorbent.
Reaction Rate Uniform rate Increases slowly and attain equilibrium
Types Either physical or chemical Either chemisorption or physisorption 
Energy Ions or atoms get absorbed within the space of the absorbent. The adsorbate binds on the surface of the adsorbent by the interaction of van der wall forces or covalent bonds.
Limiting factors The flow rate in water, the composition of water, operating pressure, and temperature Time of contact, characteristic of adsorbent, the solubility of adsorbate, surface area, size, pH, and temperature
Application Refrigerants, cold storage, cooling system, and ice production Water purification, air conditioning, and synthetic resin

What is Absorption?

Absorption is a process by which one substance permeates and is assimilated into the bulk of another substance. Unlike adsorption, which involves molecules adhering to the surface of a material, absorption entails the penetration of the absorbing substance into the interior of the absorbent material. This process typically occurs in liquids or solids and can involve gases, liquids, or solutes being taken up by a solid or liquid medium.

The mechanism of absorption relies on the movement of molecules from an area of higher concentration to an area of lower concentration, often through diffusion. The absorbed substance is then distributed and incorporated into the structure of the absorbent material. A common example of absorption is the way a sponge soaks up water, with the liquid being drawn into the porous structure of the sponge.

In biological contexts, absorption is a vital process for nutrient uptake by living organisms. In plants, for instance, roots absorb water and essential nutrients from the soil. In summary, absorption is characterized by the internal assimilation of one substance by another, contributing to the distribution and incorporation of the absorbed material within the bulk of the absorbent medium.

What is Adsorption?

Adsorption is a surface phenomenon in which molecules or particles adhere to the surface of a solid or liquid material without penetrating its interior. This process occurs due to attractive forces between the adsorbate (the substance being adsorbed) and the adsorbent (the material with the surface to which the adsorbate adheres). These attractive forces can include van der Waals forces, electrostatic interactions, or even chemical bonding.

The mechanism of adsorption involves the concentration of the adsorbate on the outer layer of the adsorbent material, creating a thin film or layer. Unlike absorption, adsorption does not involve the substance permeating or diffusing into the bulk of the adsorbent. Instead, the molecules accumulate on the surface, forming a layer that can be physically or chemically bound.

Activated charcoal is a notable example of a material that exhibits strong adsorption properties. It possesses a highly porous structure that provides a large surface area for molecules to adhere to, making it effective in adsorbing impurities from gases or liquids. Adsorption plays a crucial role in various industrial processes, including catalysis, gas purification, and water treatment, where the selective adherence of molecules to a surface is exploited for practical applications.

Main Difference Between Absorption and Adsorption 

  1. Absorption is the process whereby a substance is taken in the bulk of another substance whereas adsorption is the process whereby adsorbate sticks on the surface of the adsorbent.
  2. The reaction rate in absorption is endothermic and uniform while adsorption is exothermic and increases slowly to attain equilibrium.
  3. The concentration of absorbate in the absorption process remains constant throughout the medium while adsorbate in the adsorption process changes from bulk to the bottom of the adsorbent.
  4. Adsorption is affected by temperature and it works well under low temperature whereas absorption is not affected by temperature.
  5. The absorption process is applicable in Ice production, cooling systems, and cold storage while the adsorption process is applicable in air conditioning, water purification, and synthetic resin.
  6. The absorption is comparatively slower and equilibrium take more time to be attained whereas adsorption is rapid and equilibrium occur faster
  7. Absorption occurs at a uniform rate whereas adsorption increase steadily
  8. Absorption is a bulk phenomenon whereas adsorption is a surface phenomenon 
  9. The concentration of absorbate is the same throughout the absorbent in absorption whereas the concentration of adsorbate is more at the surface than other parts of the adsorbent in the adsorption

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Conclusion

Absorption and adsorption are distinct processes with unique characteristics in their interactions with substances and surfaces. Absorption is characterized by the penetration of one substance into the bulk of another, commonly involving the uptake of liquids or gases by solids or liquids. This process relies on the diffusion of molecules into the interior of a material, where they are assimilated and distributed throughout.

In contrast, adsorption occurs when molecules adhere to the surface of a solid or liquid material without penetrating its interior. The interaction takes place on the surface, where molecules are attracted through forces such as van der Waals forces, electrostatic interactions, or chemical bonding. Activated charcoal provides a practical example of adsorption, as it adheres to impurities in liquids and gases on its surface.

In essence, the key distinction lies in the depth of penetration and location of the interaction. Absorption involves the internal assimilation of substances, whereas adsorption entails the adhesion of molecules to the surface without entering the material’s interior. Both processes find applications in diverse fields, from industrial processes to environmental remediation, highlighting their significance in various practical contexts.

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