Adsorption : Definition, Types and Factors Affecting.

Adsorption

is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface. This process creates a film of the adsorbate on the surface of the adsorbent. This process differs from absorption, in which a fluid is dissolved by or permeates a liquid or solid.

Reversible and irreversible adsorption

The adsorption is reversible, if the adsorbent can be easily removed from the surface of the adsorbent by physical

methods. It is called irreversible adsorption, if the adsorbate can not be removed from the surface of the

adsorbent.

A gas adsorbed on a solid surface can be completely removed in vacuum. It is, therefore, reversible adsorption.

Examples of irreversible adsorption are adsorption of oxygen on tungsten adsorbate and adsorption of CO on

tungsten surface 

Adsorbent, Adsorbate and Interface

● The substance upon whose surface the change of concentration occurs, is called absorbent.

● The substance taken up on the surface is called adsorbate.

● The common surface between the two phases where the adsorbed molecules concentrate is called the

interface.

Factors Affecting Adsorption:

● Temperature: An increase of temperature leads to a decrease in amount adsorbed and vice – versa.

● Pressure or concentration: It has been found that in most cases, the adsorption is reversible and an increased pressure of a gases vapour or an increase in concentration of a solute causes increased adsorption.

● Nature of Adsorbate and Adsorbent: The amount of the gas absorbed depends upon the nature of adsorbent and the gas (adsorbate), which is to be adsorbed. It has been found that easily liquefiable

gases such as NH3, HCl, Cl2 , SO2 CO2 etc. are more readily adsorbed than the so called permanent gases such as O2,N2, H2 etc. This is because molecules of the former type of gases have greater Vander

waal’s or molecular force of attraction.