Difference Between Absorption and Adsorption (With Table)

Chemistry deals with all kinds of reactions and the chemical science behind everything. From a basic structure to the reactions happening between any two or more substances, everything could be explained using chemistry. In chemistry, some of the words may have a similar sound but could mean something totally different. One such example seen is absorption and adsorption.

Both absorption and adsorption are chemical processes widely used in chemistry as well as in daily life. Simple processes could show the phenomenon of absorption or of adsorption and can be a great source of examples to understand the phenomenon. While both of them can sound similar, both the terms are different with respect to the chemical processes and their applications.

Absorption vs Adsorption  

The main difference between absorption and adsorption is that absorption is a process involving chemical interactions while adsorption is a phenomenon involving the attraction of molecules that are present on a substance’s surface. Absorption allows the chemical bonding of the molecules whereas adsorption allows the substance to be loosely attached to a surface.

Absorption is a phenomenon where one substance can enter into another substance’s bulk or volume. It allows the molecules, atoms, or ions to be absorbed in other substances bulk and often leads to the formation of a third component. There are two types of absorption namely, chemical absorption and physical absorption. Both of them follow the general principle of absorption but differ in the bonding of the components.

Adsorption is a surface phenomenon where the substance or say the molecules, atoms, or ions are attached to the surface of another component, usually being solid. Adsorption is also of two types, namely physical adsorption, and chemical adsorption. The difference in both is the types of attractive forces acting between the two components i.e. the adsorbent and the adsorbate. 

Comparison Table Between Absorption and Adsorption  

Parameters of ComparisonAbsorptionAdsorption
MeaningOne substance enters into the bulk of another substance.One substance adheres to the surface of the other substance.
PhenomenonBulk phenomenonSurface phenomenon
ReactionEndothermic reactionExothermic reaction
ProcessIrreversibleReversible
Temperature co-relationNot relatedWorks great in lower temperature conditions
Rate of reactionUniform rate of reactionInitially, the rate of reaction increases and reaches equilibrium.
ExamplesPaper soaked in water, sponge soaked in any liquid.Charcoal in a gas mask, Salts in a desiccator.
ApplicationProduction of ice, cold storage, etc.Purification of water, Air conditioning, etc.

What is Absorption?

Absorption is the phenomenon of taking a substance by another substance into its bulk. The acceptance of molecules, ions, or atoms by another substance into its bulk can be called absorption. This is a bulk phenomenon and requires heat energy for processing. The requirement of heat for the process makes absorption an endothermic process. In the continuation of the process, a new substance may be formed as a result of a reaction between the components.

Absorption has two main components namely, the absorbent and the absorbate. The absorbent is the substance having spaces or voids in them which helps them to take up another substance into its bulk. The absorbate is the substance being absorbed. It gets absorbed and occupies the spaces or voids present in the absorbent. They can interact physically or via a chemical reaction i.e. chemically. This is an irreversible process and cannot be separated easily.

Absorption types: Chemical Absorption and Physical Absorption.

Chemical Absorption takes place when the absorbate and absorbent react chemically i.e. a chemical reaction happens between them. Chemical absorption is concentration-dependent and dependents directly on the concentration of reactants. Physical absorption takes place according to Henry’s Law. Physical absorption is a non-reactive process and depends upon the physical properties of the absorbate.

What is Adsorption?

Adsorption is a phenomenon of attachment of a substance to the surface of another substance. The acceptance of molecules, ions, or atoms by another substance on its surface can be called adsorption. This is a surface phenomenon and liberates energy during the process. The liberation of energy for the process makes adsorption an exothermic process. Adsorption directly depends on the concentration of the adsorbate being adsorbed.

Adsorption has two main components namely, the adsorbent and the adsorbate. The adsorbent is the substance that offers its surface for other substances to adhere to it and get adsorbed. The adsorbate is the substance being adhered to a surface. They can interact physically or via a chemical reaction i.e. chemically. This is a reversible process and can be separated easily, the separation process is called desorption.

Adsorption types: Chemical Adsorption and Physical Adsorption.

Chemical Adsorption or Chemisorption takes place when the adsorbate and adsorbent react chemically i.e. a chemical reaction happens between them. One of the common examples of chemisorption is corrosion. Physical adsorption or Physisorption takes place when the adsorbate and adsorbent develop weak forces such as Vander Waal forces between them. Examples- Adsorption of gases onto the surface of the charcoal.

Main Differences Between Absorption and Adsorption

  1. Absorption is where one substance enters into the bulk of another substance while adsorption is a phenomenon where one substance adheres to the surface of the other substance.
  2. Absorption is a bulk phenomenon whereas adsorption is a surface phenomenon.
  3. Absorption is an endothermic reaction i.e. requires energy while adsorption is an exothermic reaction.
  4. Adsorption works great in lower temperature conditions whereas temperature does not affect absorption.
  5. Adsorption is concentration-dependent whereas absorption is not.
  6. Absorption has a uniform rate of reaction while in the case of adsorption the initial rate of reaction increases and slowly reaches equilibrium.

Conclusion

Both absorption and adsorption are similar sounding words and is classic example of homophones. Both of them are different processes, have different chemistry and applications in daily life. Absorption is a process relating to the incorporation of the substance into other substance bulk. Adsorption is related to the surface attachment of a substance to another substance’s surface. Both of the processes are quite opposite in nature and are totally different phenomena having different applications in the modern-day.

References

  1. https://pubs.acs.org/doi/abs/10.1021/la991515a
  2. http://yadda.icm.edu.pl/yadda/element/bwmeta1.element.baztech-article-BGPK-2858-1091