Difference Between Adsorb and Absorb

Even though these two words may sound similar, they cannot be used interchangeably especially when it comes to sciences like physics and chemistry. In everyday use, however, we do not care for these technicalities and just use either of them 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 in simple terms 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.

Adsorb vs Absorb

The main 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 while the former is a surface phenomenon and the gas or liquid only adheres to the surface of the second matter. 

Adsorb vs Absorb

Comparison Table Between Adsorb and Absorb

Parameters of comparison AdsorbAbsorb
DefinitionAssimilation of the molecules of the gas or liquid 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 PhenomenonBulk phenomenon.Surface phenomenon.
Heat ExchangeEndothermic processExothermic process.
Distribution of ConcentrationThroughout the bulk of the material, the concentration of the absorbed material is distributed.Only on the surface of the adsorbent material the concentration more.
Affected byThe volume of the substance.The Surface area of the substance.
ExamplePurification 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 and 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 types of absorption which are physical absorption and chemical absorption. In the former type, there are no chemical reactions or chemical bonds formed between the absorbate and absorbent, but in the latter one the chemical absorption, there is an active chemical reaction and chemical bond formation.

There is another phenomenon known as absorption spectroscopy which measures the radiation on the basis of frequency and wavelength, and that too is an essential process to determine the certain percent of substances in the sample. Examples of absorptions include purification of water through the use of alum, removing hardness of water, 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 to undergo the process is less and the bonds thus formed between the adsorbate and adsorbent is also weak. It is also affected by the surface area, the temperature of the process.

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 gets assimilated 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 most of the time. 

Conclusion

Thus the difference between adsorb and absorb is that one is a surface phenomenon and the other is a bulk phenomenon. So even though the differences are not interchangeable they cannot be perceived by the naked eye as the interaction is between the atoms and molecules of the two materials.

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
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