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Difference between Absorption and Adsorption

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Last updated date: 19th Feb 2024
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What is Absorption and Adsorption: Introduction

Absorption and adsorption are two important processes that occur in our daily lives, often without us realizing it. These processes play crucial roles in various fields, including chemistry, materials science, environmental studies, and even our everyday activities. Understanding the concepts of absorption and adsorption can help us comprehend the world around us and make informed decisions. In this article, we will explore the definitions, mechanisms, and absorption and adsorption examples, highlighting their significance in different applications. 


What is Absorption? 

Absorption is the process by which one substance is taken up and incorporated into another substance, typically involving the penetration of molecules into the bulk of the absorbing material. It occurs when the absorbing material has the ability to draw and retain other substances within its structure. The absorbed molecules become uniformly distributed throughout the volume of the absorbing material.


Example of Absorption: A common real-life example of absorption is the process of soaking a sponge with water. When a dry sponge comes into contact with water, the water molecules are drawn into the sponge's porous structure and distributed evenly throughout its volume. This is because the sponge material has the ability to absorb water, allowing it to hold a significant amount of liquid within its structure. Other examples of absorption include the absorption of ink by paper, the absorption of moisture by desiccants, and the absorption of nutrients by plant roots. 


What is Adsorption? 

Adsorption is the process by which molecules adhere to the surface of a solid or liquid material, forming a thin film or layer of the adsorbed substance. Unlike absorption, adsorption does not involve the penetration of molecules into the bulk of the adsorbent material. Instead, it occurs due to attractive forces between the molecules and the surface of the adsorbent.


Example of Adsorption: A practical example of adsorption is the use of activated carbon filters in water purification systems. Activated carbon has a highly porous structure with a large surface area, providing numerous sites for the adsorption of impurities and contaminants from water. When water passes through the activated carbon filter, organic compounds, chemicals, and pollutants adhere to the surface of the activated carbon through adsorption. This process helps to remove impurities and improve the quality of the water. Another example of adsorption is the adsorption of gases, such as nitrogen or carbon dioxide, on the surface of activated charcoal in gas masks or air purifiers.


Characteristics of Absorption and Adsorption

Mechanism: The primary distinguishing characteristic between absorption and adsorption is the mechanism by which molecules interact with the material. In absorption, molecules are taken up into the bulk of the material and distribute themselves uniformly throughout its volume. In adsorption, molecules adhere to the surface of the material without penetrating into its bulk.


Distribution: Absorption results in a uniform distribution of molecules throughout the absorbing material's volume. In contrast, adsorption leads to a concentrated layer of molecules adhered to the surface of the adsorbent material.


Reversibility: Absorption is generally a reversible process, and molecules can be released from the absorbing material under appropriate conditions. Adsorption, on the other hand, can be reversible or irreversible, depending on the strength of the interactions between the molecules and the adsorbent surface.


Applications of Absorption and Adsorption

Absorption and adsorption have diverse applications across various industries.


Absorption finds applications in gas separation processes, where it is used to remove impurities from gas streams. It is employed in natural gas processing to eliminate substances like carbon dioxide and hydrogen sulfide. In air conditioning and dehumidification systems, absorption is utilized to cool air and remove moisture, ensuring comfortable indoor environments. The pharmaceutical industry utilizes absorption in drug formulation to enhance the bioavailability of drugs and control their release profiles. Environmental remediation efforts employ absorption to remove pollutants from soil and water, with activated carbon being a commonly used absorbent material.


Adsorption is widely used in water and air purification systems, where activated carbon filters adsorb impurities and contaminants, improving water and air quality. Catalysis heavily relies on adsorption to bind reactant molecules onto catalyst surfaces, enhancing chemical reactions. Adsorption is also employed in gas storage applications, such as storing hydrogen and methane, and in gas separation processes. Additionally, chromatography relies on the differential adsorption of components to separate and analyse mixtures. 


The applications of absorption and adsorption span various industries, including environmental, chemical, pharmaceutical, and energy sectors. These processes contribute to advancements in technology and play crucial roles in ensuring cleaner and safer environments.


Differences between Absorption and Adsorption

Sr. No.

Characteristics

Absorption

Adsorption

1

Definition

The process of one substance being taken up and distributed within the structure of another substance.

The process of molecules adhering to the surface of a solid or liquid, forming a thin film. 

2

Mechanism

Absorbed substance penetrates the bulk of the absorbing material.

Adhered substance remains on the surface of the adsorbent material.

3

Penetration

Absorbed substance can penetrate into the interior of the absorbing material.

Adhered substance does not penetrate the surface of the adsorbent material.

4

Driving Force

Generally driven by solubility and diffusion processes.

Driven by surface interactions, such as electrostatic forces, van der Waals forces, or chemical bonding.

5

Nature of Interaction

Absorbed substance and absorbing material often interact chemically or physically.

Adsorbed substance adheres to the surface of the adsorbent material without a strong chemical or physical interaction.

6

Reversibility

Absorption is generally reversible.

Adsorption can be reversible or irreversible, depending on the nature of the adsorbate-adsorbent interaction.

7

Examples

Absorption of water by a sponge

Adsorption of pollutants by activated carbon

8

Applications

Gas separation, drug formulation, air conditioning, environmental remediation

Water purification, catalysis, gas storage, chromatography


Summary

Absorption and adsorption are two distinct processes that occur in various aspects of our lives. Absorption involves the incorporation of molecules into the bulk of a material, leading to a uniform distribution throughout its volume.


Adsorption, on the other hand, involves the adhesion of molecules to the surface of a material, forming a concentrated layer. Understanding these processes and their real-life examples can deepen our knowledge and appreciation of the natural and engineered systems around us.

FAQs on Difference between Absorption and Adsorption

1. What is the difference between absorption and adsorption? 

Absorption is the process where one substance is taken up and distributed within the structure of another substance, penetrating its bulk. On the other hand, adsorption refers to the process where molecules adhere to the surface of a solid or liquid, forming a thin film without penetrating the surface. 

2. Can absorption and adsorption occur simultaneously? 

Yes, absorption and adsorption can occur simultaneously in certain cases. For example, when a liquid is absorbed by a porous material, it can simultaneously undergo absorption into the material's bulk and adsorption onto its surface. The relative contributions of absorption and adsorption depend on factors such as the properties of the substances involved and the conditions of the system. 

3. What are some common applications of absorption and adsorption? 

Absorption and adsorption have various practical applications. Absorption is widely used in gas separation processes, such as removing carbon dioxide from flue gases in power plants. It is also utilised in drug formulation to enhance the bioavailability of pharmaceuticals. Adsorption finds applications in water purification, where activated carbon is used to remove impurities and contaminants. It is also essential in catalysis, where solid catalysts adsorb reactant molecules to facilitate chemical reactions. Additionally, adsorption is employed in gas storage systems and chromatography techniques for analytical separations.