Question

Which of the following is not a favourable condition for physical adsorption?
A. Higher critical temperature of adsorbate
B. Low temperature
C. High pressure
D. High temperature

Answer 1

Hint: We know that adsorption is the process of higher concentration of any molecular species at the surface than in the bulk of a solid. In physical adsorption the adsorbate molecules are held by weak van der Waals forces. Hence, the activation energy of desorption is very low.

 Complete step by step answer:
A decrease in surplus forces of the surface occurs during adsorption, i.e., there is a reduction in surface energy which resembles heat. In solid the quantity of gas consumed depends on the nature of gas. In general, gases with greater critical temperatures are adsorbed readily because near the critical temperatures van der Waals’ forces are more powerful.
With increase in pressure more gas is consumed in adsorption. When pressure increases the volume of the gas decreases (By Le–Chateliers’s principle) and the gas can be removed by decreasing pressure.
Physical adsorption occurs at very low temperatures. With rise in temperature physisorption decreases. Therefore, among them high temperature is not a favourable condition for physical adsorption.
Hence, the correct option is D.

Additional Information:
According to the substances deposited and adsorbed adsorption is classified into two ways. They are physical (physisorption) and chemical adsorption (chemisorption). A multimolecular layer results in Physisorption while in chemisorptions a unimolecular layer results.

Note:
A student gets confused between adsorbate and adsorbent. The substances which are deposited on another substance's surface is known as adsorbate and the surface on which adsorbate adsorb is known as adsorbent.