Question

Which one of the following is not a property of physical adsorption?
A.Lower the temperature, more the adsorption
B.greater the surface area, more the adsorption
C.Higher the pressure, more the adsorption
D.Unilayer adsorption occurs

Answer 1

Physical adsorption involves the accumulation of the adsorbate on the adsorbent on account of weak Van der Waals forces. No strong attraction or bond formation is present between the adsorbent and adsorbate.

Complete step by step solution:
Physical adsorption is non-specific in nature as there are no significantly strong attractions between the solute and solvent. Any gas can be adsorbed on the surface of a solid to some extent or other. However, it is evident that an easy liquefiable gas like ammonia is adsorbed more than permanent gases like nitrogen.
Since adsorption is accompanied by the release of heat energy, so in accordance with Le-Chatelier’s principle, we can say that the increase in temperature decreases the extent of adsorption and vice versa.
The specific area of an adsorbent is the surface area that is available for adsorption per gram of adsorbent. It can be concluded that greater the surface area of adsorbent, greater will be the extent of adsorption.
As we know that physical adsorption is reversible, we can say that it is accompanied by a decrease in pressure. Thus, it is expected that at a constant temperature, the extent of adsorption will increase with the increase in the pressure of the gas.
Since there are no specific bonds between the adsorbent and adsorbate, multi-layer adsorption can take place.

Thus, we can conclude that the incorrect statement is D.

Note: The other type of adsorption is known as chemical adsorption or chemisorption. Unlike physical adsorption, chemisorption involves the formation of chemical bonds between the adsorbent and adsorbate. As a result, it is highly specific in nature and irreversible. A physical adsorption at low temperature may pass into chemisorption as the temperature is increased.