Absorption and Adsorption

Adsorption and absorption are important for physical and chemical processes with practical applications in making life safer and better.

Adsorption and absorption are the two most prevalent surface chemical processes. The distinctions between adsorption and absorption are frequently misunderstood. Atoms travel through or enter a substance during the absorption process. On the other hand, adsorption holds molecules loosely on the adsorbent’s surface and allows them to be easily removed. When atoms, ions, or molecules are attached to the surface of the adsorbent, it is called adsorption.

Adsorption is the action of atoms, molecules, or ions of an adsorbate sticking to the surface of an adsorbent.

Absorption is the action of a fluid medium (the absorbate) absorbed or soaked into the surface of an absorbent.

Adsorption and absorption happen at the same time :-

If both adsorption and absorption take place at the same time, the phenomenon is known as sorption. As a result, sorption entails the collection of molecules on a solid or liquid surface. The material that binds to the sorbent is called sorbate.

Sorption can be shown in the following examples:

A sponge dipped in water. When we dip the sponge in water, water molecules form a film on the sponge’s layer. Then the water molecules start getting inside the sponge’s bulk, resulting in simultaneous adsorption and adsorption.

Cotton fibres are stained using azo dyes through a sorption process.

Absorption vs Adsorption

The processes of absorption and adsorption are very different. Only thing that is common in both the processes is that molecules or atoms move from one to another region.

Absorption

Absorption is a bulk event in which two separate substances join, as we’ve seen. The following are some of the additional distinctive properties of absorption:

• Endothermic process – Absorption is an endothermic process requiring energy input. During absorption, the energy of the absorbate is added to the energy of the absorbent system, increasing the overall energy of the system.
• It absorbs at a constant rate – The absorbent absorbs the absorbate at the same rate until it is completely dissolved in the absorbent.
• It generates a homogeneous concentration – After the absorption process, the adsorbate concentration in the absorbent is uniform.
• It is temperature independent – The temperature at which absorption takes place has no bearing on the pace or efficiency of the operation.

Adsorption

Adsorption differs from absorption in that it occurs on the surface. The two different chemicals do not mix; instead, the adsorbate accumulates on the adsorbent’s surface. Other distinguishing characteristics of adsorption include:

• Adsorption is exothermic – The adsorption mechanism is exothermic, which means it produces heat. As the adsorbate particles condense on the surface of the adsorbent, the system becomes more stable, resulting in a decrease in energy. As the excess energy is released, the process becomes exothermic.
• The rate rises – The adsorption rate rises steadily until it reaches equilibrium and stops.
• There are varied, non-uniform concentrations – Because there is no dissolving and bulk action, the concentrations of adsorbate and adsorbent are diverse. The concentration at the system’s surface is different from the adsorbent’s concentration.
• It works better at low temperatures – nevertheless, the two types of adsorption, chemical and physical adsorption, act differently. When it comes to physical adsorption, the kinetic energy of the adsorbate particles increases as the temperature of the system rises. They are less likely to attach to the adsorbent’s surface when this happens.

Different types of adsorption

Adsorption is classified into two forms based on the type of bonds produced between adsorbate and adsorbent molecules: physisorption and chemisorption.

Physisorption: It is a kind of adsorption in which the Van Der Waals force forms a weak physical link between the gas molecules of the adsorbate and the solid or liquid molecules of the adsorbent. There is no chemical change, and the electronic structure of the atoms and molecules is not disturbed in this sort of connection. Hydrogen gas, for example, is adsorbed on the surface of the charcoal.

Chemisorption: It’s a sort of adsorption in which the adsorbate forms strong chemical connections with the adsorbent’s surface. The electronic structure of atoms and molecules is disrupted during chemisorption; for instance, rusting.

Different Types of Absorption

Physical Absorption: It is a type of absorption in which the molecules of absorbate and absorbent do not react. Weak physical connections cause absorption, for example, oxygen gas absorption in water.

Chemical Absorption: It’s a type of absorption in which the molecules of the absorbate and absorbent react chemically. Food digestion is the best example of chemical absorption.

Conclusion

In a nutshell, both adsorption and absorption are aspects of surface chemistry, but their mechanisms of action differ. Adsorption occurs when adsorbate molecules are attracted to the surface of the adsorbent, whereas absorption happens when absorbate molecules are entirely absorbed into the absorbent.

As a result, adsorption is a surface phenomenon, while absorption is a bulk occurrence. Various technologies, such as refrigeration system adsorption, have been developed based on these processes, and further research is ongoing to develop these surface phenomena for future usage.