Question

Point out the wrong statement, Physical adsorption is characterised by
A. Attraction occurs due to weak van der Waals forces
B. Irreversible nature of adsorption
C. Multi molecular adsorption layers
D. Decrease in adsorption with an increase in temperature

Answer 1

Hint: This is a theory-based question and the theory here used is as follows. This question entirely deals with the characteristics of physical adsorption. Physical adsorption is a simple approach, which attaches the target substance to a chip as a result of hydrogen bonding, van der Waals forces, and hydrophobic interactions. It is also known as Physisorption.

Complete Step by Step Solution:
The characteristics of Physical adsorption are
1. It is not specific in nature. Hence any gas can be adsorbed onto the surface
2. It has been observed that highly liquefiable gases are physically adsorbed more strongly.
3. It is reversible and is dependent on the pressure as well as temperature. The rise in pressure reduces the volume of gas and thus increases the adsorption of gas molecules. Conversely, a reduction in pressure will cause the removal of gas molecules from the solid surface.
4. Since the adsorption process is exothermic, the physical adsorption occurs readily at low temperatures and decreases with increasing temperatures (Le-Chatelier’s principle).
5. Porous substances are better adsorbents. Since an increased surface area promotes adsorption.
6. Does not require energy for activation.
Hence the correct option is B.

Note: Physical adsorption phenomenon involves the use of weak Van der Waal forces by means of which gas molecules get adsorbed on a solid surface. 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.