Question

Extent of physisorption of gas increases with:
A. Increase in temperature
B. Decrease in temperature
C. Decrease in surface area of adsorbent
D. Decrease in strength of van der Waals forces

Answer 1

Hint: We have studied that physisorption is a general phenomenon which happens if a solid area is brought into contact with an absorbable gas. The intermolecular forces involved are very similar as those are responsible for the condensation of the vapours and the imperfection of actual gases present. Physisorption is a process in which electronic structure of an atom or a molecule is scarcely disrupted upon adsorption, also called physical adsorption.

Complete step by step answer:
If gas accumulation occurs on the surface of a solid due to weak forces of van der Waals, the adsorption is called physical adsorption or physisorption.
Physisorption's different characteristics are—
1.It arises on account of the forces of van der Waals.
2.In nature, it is not unique.
3.It is reversible.
4.The essence of gas depends on it. Easier liquefiable gases are readily absorbed.
5.The adsorption enthalpy is low
For adsorption, the low temperature is favourable. This decreases as the temperature increases.
No appreciable activation power is needed.
It depends on the region on the surface. With an increase in surface area, that increases.
On an adsorbent surface under high pressure, this results in multimolecular layers.
Option B is correct as Extent of physisorption of a gas does increase with decrease in temperature.

So, the correct answer is Option B.

Note: For our knowledge, physisorption does not result in changes in the chemical bonding structure as opposed to chemisorption, in which the electronic structure of bonding atoms or molecules is modified and covalent or ionic bonds form. In practise, the categorization of a specific adsorption as physisorption or chemisorption depends primarily on the adsorbate's binding energy to the substrate, with physisorption being much weaker on a per-atom basis than any chemical bond-related form of bond. With decreases in temperature, the degree of physisorption of gas increases. Since physisorption particles are held to the surface by the weak attraction force of van der Waals, they are also easily desorbed at increasing temperature. Van der Waals is the basic interacting force of physisorption (VDW). Physisorption plays an important role in nature, even though the interaction energy is very small (10-100 meV). For example, the attraction of van der Waals between surfaces and gecko foot-hairs provides the remarkable ability to climb up vertical walls. Van der Waals forces derive from the interactions between electrical dipoles that are caused, permanent or temporary.