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Adsorption and absorption are two kinds of a process called sorption. They have both physical and chemical effects on other substances. They occur due to diffusion and forces of attraction between particles or molecules. Both are reversible in different conditions. Both the processes have a number of applications and industrial uses. However, adsorption and absorption are different from each other in many aspects.
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Key Terms: Sorption, Absorption, Adsorption, Endothermic Process, Exothermic Process, Desorption, Reverse Saturable Absorption
What is Sorption?
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Sorption is a physical and chemical process by which one substance becomes attached to another substance. It is of two types - absorption and adsorption. An example of sorption is a sponge dipped in water, a filter dipped in a medium, soaking up contaminants until they run out of the surface area.
Absorption and Adsorption
Difference Between Absorption & Adsorption
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The key differences between absorption and adsorption are given below:
| Parameter | Absorption | Adsorption |
|---|---|---|
| Definition | The process of any substance (atoms, ions, or molecules) taken up by or absorbed by another substance, especially in the solid or liquid material is called absorption. | The process of accumulation of any substance (atoms, ions, or molecules) to the surface of the other substance, especially in the solid, liquid, or gas medium is called adsorption. |
| Substance | The substance whose molecules are absorbed in the medium is called an absorbate. The substance in the medium in which the process takes place is called the absorbent. | The substance whose molecules are adsorbed at the surface is called an adsorbate. The substance on the surface of which the process takes the place is called the adsorbent. |
| Process media | Absorption involves the entire volume of the absorbing substance. Molecules undergoing absorption are drenched by the length, not by the air. | Adsorption is a surface-based process wherein a film of adsorbate is formed on the surface. The molecules in adsorption accumulate only on the surface but do not enter the bulk of the adsorbing substance. |
| Type of phenomenon | It is a bulk phenomenon. | It is a surface phenomenon. |
| Effect | Physical or chemical effect | Physical or chemical effect |
| Type of chemical reaction | It is an endothermic process. | It is an exothermic process. |
| Rate of reaction | The rate of reaction is uniform. | The rate of reaction increases slowly and attains equilibrium. |
| Concentration | It does not change its concentration throughout the medium. | It does not change its concentration. It varies from bulk to the bottom of the absorbent. |
| Temperature effect | No effect of temperature on absorption. | Adsorption works at a lower temperature. |
| Mechanism | The process of absorption in living systems is by passive diffusion, facilitated passive diffusion, active transport, and pinocytosis. | Adsorption occurs when the surface of the particles of absorbent is not in the same environment as the particles within the bulk. All of the forces acting between the particles in the absorbent are mutually balanced. On the surface, the particles are not surrounded on all sides by atoms or molecules of the same kind. So, the particles have unbalanced or residual attractive forces. These adsorbent forces cause the attraction of adsorbate particles onto their surface. |
| Reverse process | The reverse process is called reverse saturable absorption (RSA) or reversible saturable absorption. | The reverse process of adsorption is desorption. Here the adsorbed substance is removed from the surface of the adsorbent. |
| Types | Absorption can be classified as physical absorption and chemical absorption as per the changes. | Adsorption can be classified as physisorption (weak van der Waals forces act) and chemisorption (covalent bonding occurs). |
| Examples | Absorbent books, bath mats, cotton wool, foam pads, paper towels, towels. | Activated carbon, alumina gel, graphite, silica gel and zeolites |
| Application | Absorption chillers, cold storage, ice production, turbine inlet cooling, refrigerants, clean-burning fuels, space cooling, hydrogenation of oils, carbonation of beverages, etc. | Air conditioning, adsorption chillers, water purification, synthetic resin, chillers, a means to prolong neurological exposure to specific drugs, non-stick coatings and in various biomedical devices, etc. |
Things to Remember
- The process of any substance taken up by or absorbed by another substance is called absorption.
- The process of accumulation of any substance to the surface of the other substance is called adsorption.
- Absorption is an endothermic process whereas adsorption is an exothermic process.
- Adsorption is classified into two types: physisorption and chemisorption.
- Absorbent books, bath mats, cotton wool, foam pads, paper towels, towels are commonly used as absorbents.
- Adsorbents include activated carbon, alumina gel, graphite, silica gel and zeolites.
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Sample Questions
Ques. What is sorption? What are its two kinds? (2 Marks)
Ans. Sorption is both a physical and chemical process by which one substance gets attached to another substance. It is of two types - absorption and adsorption.
Ques. What are the examples of sorption? (1 Mark)
Ans. An example of sorption is a sponge dipped in water, a filter dipped in a medium, soaking up contaminants until they run out of the surface area.
Ques. Define absorption and adsorption. (3 Marks)
Ans. Absorption: The process of any substance (atoms, ions, or molecules) taken up by or absorbed by another substance, especially in the solid or liquid material is called absorption.
Adsorption: The process of accumulation of any substance (atoms, ions, or molecules) to the surface of the other substance, especially in the solid, liquid, or gas medium is called adsorption.
Ques. Define the terms adsorbate and adsorbent? (2 Marks)
Ans. Adsorbate is a molecule that gets adsorbed on the surface, whereas adsorbent is the surface on which adsorption takes place. Clay, colloids, silica gel, etc. are common examples.
Ques. Describe the mechanism of adsorption? (5 Marks)
Ans. The mechanism of adsorption is given below:
- Adsorption generally happens when the particle on the surface and the particle in the bulk of the adsorbent are not in the same phase or environment. The net force acting is not the same.
- The particle on the surface shows unbalanced forces called residual attractive forces
- These forces are responsible for the surface particles of the adsorbent to be attracted to the adsorbate particles
- During the process of adsorption, there will be a decrease in the residual attractive forces. The energy of the surface decreases and releases heat. This is called the heat of adsorption.
- The amount of heat released when one mole of adsorbate is adsorbed on the surface is called enthalpy of adsorption
Ques. What is the reverse process of adsorption? (2 Marks)
Ans. The reverse process of adsorption is desorption. Here the adsorbed substance is removed from the surface of the adsorbent.
Ques. What are the industrial uses of absorption and adsorption? (3 Marks)
Ans. Absorption: Absorption chillers, cold storage, ice production, turbine inlet cooling, refrigerants, clean-burning fuels, space cooling, hydrogenation of oils, carbonation of beverages, etc.
Adsorption: Air conditioning, adsorption chillers, water purification, synthetic resin, chillers, a means to prolong neurological exposure to specific drugs, non-stick coatings and in various biomedical devices, etc.
Ques. What are the important absorbents and adsorbents? (2 Marks)
Ans. Absorbent books, bath mats, cotton wool, foam pads, paper towels, towels are examples of absorbents. Activated carbon, alumina gel, graphite, silica gel and zeolites are examples of absorbents.
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