Difference Between Absorption and Adsorption

Table of Contents

Chemistry is the study of matter, as well as its properties, how substances combine to generate another substance, or how they separate, which gives rise to a third substance/substances. 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 same molecules, atoms, or ions, through the act of 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 of great importance as they lead to physical differences between similar molecules, their boiling and melting points, when the molecules change their states like from solid to liquid state, liquid to the gaseous state, or liquid to the 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.

Absorption vs Adsorption

The main difference between Absorption and Adsorption is that the former means taking or accepting molecules, atoms, or ions through a chemical reaction, whereas, the latter denotes the capability of all solid substances to attract molecules from liquid, or gaseous state, that is in contact with the surface.

Comparison Table Between Absorption and Adsorption (in Tabular Form)

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 the process of absorption.	Activated charcoal in a gas mask, is an example of adsorption.
Components	In absorption, two components are involved such as Absorbate, and Absorbent.	In adsorption, two components that are involved are 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.

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, as a result of which a new substance is formed or takes place.

The absorbing material is known as absorbate, it remains intact in other substances, which is known as absorbent due to the presence of space within the substance but they do not possess any chemical reaction with one another. Once the substance or absorbent gets absorbed into another substance, it cannot be separated easily. In Absorption, the substance gets uniformly distributed through the liquid or gaseous state. Particles of the liquid or gas get uniformly distributed throughout the body of solid.

Commercially they are used in the cooling system, cold storage, and refrigerants.

For example:

Water vapors absorbed by anhydrous CaCl2.

NH3 is absorbed in water forming NH4OH.

There are two types of absorption processes:

Chemical absorption: A chemical absorption takes place due to a chemical reaction between substances being absorbed, as well as absorbing medium. It also depends upon the concentration of the reactants.

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 is the process of keeping 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 adsorbent. It involves attraction or retention of the molecules on the surface. Adsorption involves unequal distribution in bulk and at the surface of the molecule.

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:

Water vapor adsorbed by Silica Gel.

NH3 is adsorbed by Charcoal.

The two types of adsorption processes are:

Physical Adsorption: Physical Adsorption is also known as physisorption and is caused due to weak Van der Waals force between the adsorbate and adsorbent.

Chemical Adsorption: Chemical Adsorption is also known as chemisorption and is caused due to strong chemical forces, and bonding between adsorbate and adsorbent.

Adsorption of gas on solid is a result of a spontaneous exothermic reaction. The amount of heat liberated when a unit of gas is adsorbed is called the heat of adsorption.

Main Differences Between Absorption and Adsorptionting

Absorption is a process by which atoms, molecules, or ions enter into a bulk. Whereas, the Adsorption is the accumulation of the molecular species at the surface not in the bulk.

Absorption is an endothermic process, whereas Adsorption is an exothermic process.

Absorption is a bulk phenomenon, on the contrary, Adsorption is a surface phenomenon.

The process of Absorption remains the same throughout the material, whereas, the Adsorption is a process that is determined by the concentration of the substances.

The process of Absorption occurs at the same or uniform rate, on the other hand, the process of Adsorption is rapid in the beginning and ultimately slows down.

Conclusion

Absorption and Adsorption are homophones, which means they may sound similar but possess different meanings, as well as, application. They both are a part of Chemistry, Physics, and Biology, as in all of the three branches of science they play an important role but are distinct.

Absorption is the process of absorbing or assimilating or incorporating molecules or other particles due to a chemical, or a molecular process, whereas, on the other hand, when the molecules, ions, or atoms from the liquid or gaseous state get attracted or connected to the surface of a molecule, the act of keeping them glued to the surface is known as Adsorption.

References

https://pubs.acs.org/doi/abs/10.1021/la991515a

https://pubag.nal.usda.gov/?page=18928&per_page=100&search_field=all_fields

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