Difference Between Adsorb and Absorb (With Table)

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. But there are significant differences between which is why we should be careful to use the correct one.

 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 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. 

Comparison Table Between Adsorb and Absorb

Parâmetros de comparação AdsorbAbsorb
DefiniçãoAssimilation 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.
Afetado porThe volume of the substance.The Surface area of the substance.
ExemploPurification 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. It is thus a bulk phenomenon and depends on the volume of the absorbent and continues uniformly with time. It does not depend on the temperature at which the process is taking place. 

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. It is an important phenomenon for various biological processes in like the diffusion of gases in our lungs, active transport of energy, and so on. Thus it is important to maintain the homeostasis of the body.

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. It is an exothermic reaction which means that heat is evolved when this process occurs. 

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. Chemical adsorption is caused by chemical forces and thus the bond formed are strong and the energy required for this is more than the physical counterpart. Also, physical adsorption is a multi-layered process whereas chemical adsorption is a single-layered one.

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. 

Conclusão

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. For example,  a sponge will absorb the liquid it is placed onto but even when one wrings out the liquid there might be some on the surface and that is due to adsorption. 

Referências

  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
x
2D vs 3D