Although the terms "absorption" and "adsorption" seem same, they have different meanings and uses. The words are used in many different contexts, and each one of them has a distinct meaning.
What distinguishes adsorption from absorption?
Absorption in physics refers to the incorporation of a gaseous component, known as the "absorbate," into the volume filled by a liquid substance, known as the "absorbent." Adsorption is the phenomena that happen when a substance, known as "adsorbate," in a liquid or gaseous state, attaches to the wall of a solid, known as "adsorbent."
Let’s discuss how adsorption and absorption differ.
What is absorption?
When one or more components of a gaseous mixture dissolve in a liquid, through the process of mass diffusion, this phenomenon is known as absorption. Because, there are no chemical changes involved, it is reversible.
Absorption is mostly employed in industry to purify gases, whether the gas is a product or a by-product of a process. It’s use is to reduce SO2 and CO2 in a gas stream, in absorption columns.
What is adsorption?
When a substance in a liquid or gaseous phase interacts with an adsorbing solid, and is physically forced to attach to its surface, this is known as adsorption (London scattering force). It is reversible as there is no exchange of e- involved.
Less frequently, chemisorption takes place, which entails irreversible changes to the chemical composition, of the adsorbent and adsorbate.
Adsorption is frequently used to clean gases and liquids. In the industrial setting, packed columns are frequently used to create a flow for the treated liquid or gas. Some examples include purifying water with activated carbon, which can attach to organic substances like pesticides and hydrocarbons, and collecting moisture from a gaseous stream by passing it through a column of activated alumina, which adsorbs the water molecule.
Difference between Adsor?ption and Absorption
Criteria |
Absorption |
Adsorption |
Definition |
Assimilation of the molecular system, throughout the bulk of the solid or liquid medium |
The accumulation of molecular species is at the bottom, instead of the liquid or solid |
Phenomenon |
A bulk phenomenon |
A surface phenomenon |
Heat exchange |
Endothermic process |
Exothermic process |
Temperature |
The temperature has no effect |
Influenced by low temperature |
Rate of reaction |
Occurs at a uniform rate |
Increases steadily and reaches equilibrium |
Concentration |
It is constant throughout the medium |
Concentration is at the bottom of adsorbent and is different from that in bulk |
Various types of adsorbents
Good adsorbents include:
· Al2O3 gel
· Inulin gel
· Zeolites
· Activated Carbon
· Graphite
How does adsorption work?
The forces acting on a substance's surface particles are different from those operating on the substance's bulk, which leads to the adsorption process. On the exposed surface, in contrast to the particles inside the bulk, the particles are not completely encircled by atoms.
As a result, while the forces on the surface are out of balance, those on the inside are in balance. The adsorbate particles tend to be drawn to the surface by the imbalanced residual forces. This triggers the adsorption process. It should be emphasised that, at a given temperature and pressure, the adsorption will be more extensive the larger the surface area of the adsorbent.
Conclusion
Although, the phrases absorption and adsorption sound alike, their applications and meanings are distinct, making it impossible to interchange or use either term at will.
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