Adsorb vs Absorb: Difference and Comparison

Even though these two words may sound similar, they cannot be used interchangeably, especially in sciences like physics and chemistry. In everyday use, however, we do not care for these technicalities and use either to mean the process of soaking up or “absorbing”; it is the more popular and well-known of the two.

 To absorb means to undergo the process of absorption, which means to soak up the liquid or gas into another fluid or solid body. To adsorb means to undergo the process of adsorption, which occurs when any material adheres to the surface of another solid material.

Key Takeaways

1. Adsorb and absorb are two different processes of molecules binding to a surface and being taken in, respectively.
2. Adsorption is the binding of molecules to a surface, while absorption is the taking in of molecules by another substance.
3. In adsorption, the surface molecules do not penetrate the adsorbent, while in absorption, the molecules penetrate the absorbing substance.

Adsorb vs. Absorb

The difference between “adsorb” and “absorb” is that the latter is a bulk phenomenon wherein the other molecules get assimilated throughout the body of the absorbent. At the same time, the former is a surface phenomenon, and the gas or liquid only adheres to the surface of the second matter. 

Comparison Table

Parameters of comparison	Adsorb	Absorb
Definition	Assimilation of the gas or liquid molecules throughout the bulk of the solid or liquid medium.	Assimilation of the molecules of gas or liquid only on the surface of the liquid or solid medium.
Type of Phenomenon	Bulk phenomenon.	Surface phenomenon.
Heat Exchange	Endothermic process	Exothermic process.
Distribution of Concentration	The absorbed material’s concentration is distributed throughout the bulk of the material.	Only on the surface of the adsorbent material is the concentration.
Affected by	The volume of the substance.	The Surface area of the substance.
Example	Purification of the gas	Painting over a surface like a wall.

What is “Absorb”?

 “Absorb” is the more popular and well-known of the two, and it is a verb used to signify the soaking up of a liquid by another material like a sponge. The material which is being absorbed is called the absorbate, while the one retaining the absorbate is called absorbent.

There are two main absorption types: physical absorption and chemical absorption. In the former type, no chemical reactions or chemical bonds are formed between the absorbate and absorbent. Still, in the latter one, the chemical absorption, there is an active chemical reaction and bond formation.

Another phenomenon known as absorption spectroscopy measures the radiation based on frequency and wavelength, which is an essential process to determine a certain percentage of substances in the sample. Examples of absorptions include water purification through alum, removing the hardness of water, and using aluminum and silica gel as drying agents. 

What is “Adsorb”?

It is the process in which the adsorbate assimilates on the surface of the adsorbent, and thus it is a surface phenomenon. Thus the concentration of the absorbate is more on the surface, and it is a temperature-dependent process as well, which means the rate of adsorption changes with temperature and is not linear.

The different types of adsorption include physical and chemical adsorption; in physical adsorption, the energy needed to undergo the process is less, and the bonds thus formed between the adsorbate and adsorbent are weak. It is also affected by the process’s surface area and temperature.

Examples of adsorption include the ion exchange method in metallurgy for the concentration of the ore, purification of air, and so on. Adsorption chromatography helps us to separate pigments and hormones. 

Main Differences Between Absorb and Adsorb

1. Absorption is a bulk phenomenon where the material assimilates throughout the body of the solid or liquid material. Adsorption is a surface phenomenon where the material adheres to the outside surface of the second medium.
2. “Adsorbing” of a material depends on the surface area of the medium, while “absorbing” of a material depends on the volume of the media.
3. Adsorption is an exothermic process, while Absorption is an endothermic process. 
4. The concentration of the absorbed material is the same throughout the bulk of the material, while in the case of adsorption, it is uneven and more on the surface.
5. Absorption is a chemical process often, while Adsorption is a physical process. 

References

1. https://link.springer.com/article/10.1007/s00467-014-2968-3
2. https://pubs.acs.org/doi/abs/10.1021/la991515a
3. https://www.sciencedirect.com/science/article/pii/S0926860X06003814

Last Updated : 29 March, 2024