Difference Between Adsorption and Absorption

Adsorption and absorption are two very similar words that tend to be confused by many people due to their very similar pronunciation. First of all, these are two physical-chemical processes in which the atoms, ions and molecules of a substance move or change their composition and shape.

Despite the above, these are two totally different words with different applications and meanings, which we will point out in this article in order to clarify any possible doubts that readers may have.


Adsorption is a physical or chemical process by which atoms, ions, or molecules are trapped or retained on the surface of a material. It can also be said that adsorption is a superficial phenomenon, since the adsorbed substance is not introduced into the volume of the body, but only adheres to its surface. So, in this process, there is a real attractive force that makes a particle adhere to another particle of another material.

Additionally, in adsorption the atoms of gaseous and liquid substances are attached to a solid surface, in some cases the atoms share electrons with the atoms of the solid substance, so that, as indicated above, a thin layer is formed but not penetrate inside.

For example: Moisture removal from compressed air is an adsorption process in which compressed air is passed through a bed of alumina or other active material, which retains water molecules.


Absorption is a physical or chemical process in which atoms, molecules or ions pass from one first phase to another, joining the volume of the second phase. Absorption can be a chemical or physical process depending on whether or not there is a chemical reaction:

  • As a chemical process, absorption is a process that separates the components of a gas from the inclusion of a solvent in the liquid state, with which it creates a solution.
  • As a physical process, absorption is a decrease in the intensity of the radiation that passes through a body, that is, it is that process of transferring energy from electromagnetic or sound waves to a medium when they pass through it or affect it.

Additionally, absorption is a volume phenomenon, since it occurs when one substance is introduced into the structure of another. In short, it can be said that absorption is a mass transfer process that consists of putting a gas in contact with a liquid, so that it dissolves certain components of the gas, leaving it free of them.

For example: Gases containing sulfur dioxide, such as boiler gases, can contact limestone to form an insoluble calcium sulfite.

As can be seen in the definitions, there are important differences between these two concepts. In summary, it can be said that:

  • Adsorption refers to the adherence of molecules to a surface while absorption refers to transfer, that is, the incorporation of molecules into another substance.
  • Adsorption is carried out in most cases with solid-liquid and solid-gas systems while absorption is carried out in liquid-liquid and liquid-gas systems.
  • Adsorption is a surface phenomenon while absorption is an incorporation phenomenon.

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