10 Difference Between Absorption And Adsorption (With Examples)

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The process of adsorption occurs due to presence of unbalanced or residual forces at the surface of liquid or solid phase. These unbalanced residual forces have tendency to attract and retain the molecular species with which it comes in contact with the surface. The process of adsorption involves two components adsorbent and adsorbate.

Absorption according to chemistry, is a physical or chemical phenomenon or a process in which atoms, molecules or ions enter some bulk phase (liquid or solid material).

When both adsorption and absorption take place simultaneously, the process can be referred to as sorption.

Definition of Terms: Adsorbate and Adsorbent

  • Adsorbent is a substance that is usually porous in nature with high surface area that can adsorb substances onto its surface with the help of intermolecular force.
  • Adsorbate is a substance that is adsorbed on the surface of another substance.

The Difference

Description

 Absorption is the process by which atoms, molecules or ions enter a bulk phase of a liquid, gas or solid. The phase in which molecules are absorbed is usually described as absorbent.

Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of adsorbate on the surface of adsorbent.

Rate

The rate of absorption maintains a steady state throughout the process. The steady state is maintained despite an increase or decrease in temperature.

The rate of adsorption is usually high in the initial stages of the process, after a few minutes, it begins to decrease until equilibrium is reached. Increase in temperature increases the rate of adsorption decreases.

 Types

Absorption can be categorized into two types:

Physical absorption: Physical absorption whereby the absorbed and the absorbent molecules do not interact with each other, and therefore, they do not perturb the chemical nature of molecules.

Chemical absorption: Chemical absorption is whereby; the absorbed and absorbent molecules chemically interact with each other, resulting in the formation of chemically distinct products.

Adsorption on the other hand can be categorized into two types:

Chemisorption: Chemisorption is whereby there are new chemical bonds that are created between the adsorbent and the adsorbate. There is usually a chemical reaction that happens between the two molecules.

Physisorption:  Physisorption is whereby there is only a force of attraction between the adsorbent and the adsorbate. In this type of adsorption, the reacting molecular species are chemically unchanged.

Type of Reaction Exhibited

In absorption, the rate of reaction is uniform and can be described as an endothermic process. Adsorption on the other hand, the rate of reaction is steady and attains equilibrium; this reaction can be described as an exothermic reaction.

Occurrence

Absorption occurs only on the surface of the phase that is in contact with the molecule. Adsorption on the contrary, occurs throughout the phase, as molecules enter and get dispersed into the phase.

Concentration

During the process of absorption, the concentration of absorbed substances does not show any significant change.  It remains constant throughout the medium.  

During the process of adsorption, the concentration of the adsorbed substance changes from bulk to the bottom of the absorbent.

Application

The concept of absorption is applied in cold storage, ice production, turbine inlet cooling, and refrigerants absorption chillers for space cooling applications. It is also used in hydrogenation of oils and carbonation of beverages.  The concept of adsorption on the other hand, is applied in air conditioning, water purification, synthetic resin, chillers and in development of non-stick coatings and in various biomedical devices.

Energy

In absorption, materials get absorbed into other material throughout the availability of space and also due to the properties of each material.

In adsorption, the adsorbates bind onto the surface of the adsorbent most commonly through Van der Waals interactions or through covalent bonds.

Examples of Adsorption and Absorption

Adsorption Examples

  1. Activated charcoal or activated charcoal is used as adsorbent with a wide range of applications. For example it is used in purification of gases and water or as an air filter in gas masks.
  2. Silica gel is also a good example of an adsorbent; it has high affinity for water and will always adsorb water more readily. For example it is widely used in many chromatographic procedures and techniques.
  3. Nickel, Platinum and palladium; these adsorbents are widely used as catalysts in many organic processes such as hydrogenation of oils.

Absorption Examples

  1. Absorption of water by sponge.
  2. Absorption of oxygen from air by water.
  3.  Purification of natural gas and other petrochemicals, whereby gases such as hydrogen sulfide and carbon dioxide are absorbed in alkanols (alcohol and amine) and eliminated.
  4. Removal of hydrogen sulfide from biogas. In this process, hydrogen sulfide is first absorbed into water and then treated with iron oxide.
  5. Absorption of ammonia by water.

Also Read: Difference Between Chemical And Physical Adsorption

Difference Between Absorption And Adsorption In Tabular Form

BASIS OF COMPARISON     ABSORPTION ADSORPTION
Description Absorption is the process by which atoms, molecules or ions enter a bulk phase of a liquid, gas or solid. The phase in which molecules are absorbed is usually described as absorbent.   Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of adsorbate on the surface of adsorbent.  
Rate The rate of absorption maintains a steady state throughout the process. The steady state is maintained despite an increase or decrease in temperature.   The rate of adsorption is usually high in the initial stages of the process, after a few minutes, it begins to decrease until equilibrium is reached. Increase in temperature increases the rate of adsorption decreases.  
Types Absorption can be categorized into two types: Physical absorptionChemical absorption   Adsorption  can be categorized into two types: Chemisorption Physisorption  
Type of Reaction Exhibited The rate of reaction is uniform and can be described as an endothermic process. The rate of reaction is steady and attains equilibrium; this reaction can be described as an exothermic reaction.
Occurrence Absorption occurs only on the surface of the phase that is in contact with the molecule. Adsorption occurs throughout the phase, as molecules enter and get dispersed into the phase.
Concentration During the process of absorption, the concentration of absorbed substances does not show any significant change.  It remains constant throughout the medium.    During the process of adsorption, the concentration of the adsorbed substance changes from bulk to the bottom of the absorbent.  
Energy Materials get absorbed into other material throughout the availability of space and also due to the properties of each material.   The adsorbates bind onto the surface of the adsorbent most commonly through Van der Waals interactions or through covalent bonds.  
Application Applied in cold storage, ice production, turbine inlet cooling, and refrigerants absorption chillers for space cooling applications. It is also used in hydrogenation of oils and carbonation of beverages. Applied in air conditioning, water purification, synthetic resin, chillers and in development of non-stick coatings and in various biomedical devices.  

Summary

Absorption is the process by which atoms, molecules or ions enter a bulk phase of a liquid, gas or solid. The phase in which molecules are absorbed is usually described as absorbent.

Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of adsorbate on the surface of adsorbent.