Absorption vs Adsorption: Difference and Comparison

Chemistry is the study of matter and its properties, how substances combine to generate another sense, or how they separate, which gives rise to a third substance/substance. All of these activities take place with the help of intermolecular forces.

Intermolecular forces, or IMF, are the forces that arbitrate interaction between different or the same molecules, atoms, or ions through either attraction or repulsion. Examples of attractive intermolecular forces are hydrogen bonding.

There are mainly four types of intermolecular forces, Ionic bonding, Hydrogen bonding, Van der Waals dipole-dipole interactions, and Van der Waals dispersion interactions. Intermolecular forces are important as they lead to physical differences between similar molecules, their boiling and melting points when they change their states from solid to liquid form, liquid to gaseous state, or liquid to gaseous state.

Absorption, in simple words, means the act of absorbing or in-take, whereas, on the other hand, adsorption is the adhesive act of holding the molecules of a liquid or a gaseous state to a surface.

Key Takeaways

1. Absorption is a process in which a substance permeates or is uniformly distributed throughout another substance, such as a liquid or gas; adsorption is the process in which molecules of a substance adhere to the surface of another substance, forming a thin film.
2. Absorption involves the complete integration of one substance into another, while adsorption involves surface interactions between substances.
3. Both absorption and adsorption involve the interaction of substances. Still, they differ in the manner and extent of the interaction, with absorption being a bulk phenomenon and adsorption occurring at surfaces.

Absorption vs Adsorption

Absorption is the process by which a substance is taken up by another substance, either by dissolving it or by permeating it through the pores of the absorbing material. Adsorption is the process by which a substance is held on the surface of another substance by weak intermolecular forces.

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Comparison Table

Parameter of Comparison	Absorption	Adsorption
Meaning	In absorption, one substance is taken up into the physical structure of another substance.	In the case of adsorption, a substance or energy is attracted to the surface of another substance.
Examples	A paper soaked in water takes up the water due to absorption.	Activated charcoal in a gas mask is an example of adsorption.
Components	In absorption, two members are involved Absorbate and Absorbent.	In adsorption, two components are involved Adsorbate and Adsorbent.
Molecules	In absorption, the molecules are drawn into the bulk of the phase.	In the case of adsorption, the molecules adhere to the surface of the phase.
Temperature	In absorption, the process is not affected by the temperature.	On the other hand, in the case of adsorption, the process is affected by temperature.

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What is Absorption?

Absorption is a bulk process of accepting molecules or other particles, such as ions or atoms, through a chemical, or a molecular reaction, resulting in a new substance forming or taking place.

The absorbing material is known as absorbate, it remains intact in other substances, known as absorbent due to the presence of space within the meaning, but they do not possess any chemical reaction with one another. Once the substance or absorbent gets absorbed into another sense, it cannot be separated easily.

They are used in cooling systems, cold storage, and refrigerants.

For example:

1. Water vapours are absorbed by anhydrous CaCl2.
2. NH3 is immersed in water, forming NH4OH.

There are two types of absorption processes:

1. Chemical absorption: Chemical absorption takes place due to a chemical reaction between substances being absorbed, as well as the absorbing medium. It also depends upon the concentration of the reactants.
2. Physical absorption: In physical absorption, the capacity of the solvent increases following Henry’s Law, and the solvent is regenerated by reducing the pressure.

 

What is Adsorption?

Adsorption keeps the molecules or other particles from the liquid or gaseous state intact with the surface. The substance being absorbed is called an adsorbate, and the solid on which the process occurs is called an adsorbent.

For example, Hydrogen (H2), Nitrogen (N2), and Oxygen (O2) get adsorbed on the surface of Charcoal. Absorption and Adsorption involve two different mechanisms.

For example:

1. Water vapour adsorbed by Silica Gel.
2. Charcoal adsorbs NH3.

The two types of adsorption processes are:

1. Physical Adsorption: Physical Adsorption is also known as physisorption and is caused due to weak Van der Waals force between the adsorbate and adsorbent.
2. Chemical Adsorption: Chemical Adsorption is also known as chemisorption and is caused due to solid chemical forces and bonding between adsorbate and adsorbent.

A gas’s adsorption on solid results from a spontaneous exothermic reaction. The amount of heat liberated when a unit of gas is adsorbed called the heat of adsorption.

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Main Differences Between Absorption and Adsorptionting

1. Absorption is a process by which atoms, molecules, or ions enter into a bulk. At the same time, Adsorption is the accumulation of the molecular species at the surface, not in size.
2. Absorption is an endothermic process, whereas Adsorption is an exothermic process.
3. Absorption is a bulk phenomenon; however, Adsorption is a surface phenomenon.
4. Absorption remains the same throughout the material, whereas Adsorption is a process determined by the concentration of the substances.
5. The process of Absorption occurs at the same or uniform rate; on the other hand, the process of Adsorption is rapid initially and ultimately slows down.

References

1. https://pubs.acs.org/doi/abs/10.1021/la991515a
2. https://pubag.nal.usda.gov/?page=18928&per_page=100&search_field=all_fields