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  • Which of the following is not a favourable condition for the physical adsorption of gas over a solid surface?Option: 1 High pressure<di

Which of the following is not a favourable condition for the physical adsorption of gas over a solid surface?

Option: 1

High pressure


Option: 2

(2) Negative \mathrm{\Delta \mathrm{H}}


Option: 3

(3) High critical temperature of gas


Option: 4

(4) High temperature


Answers (1)

best_answer

During adsorption, there is always a decrease in residual forces of the surface, i.e., there is a decrease in surface energy which appears as heat. Adsorption, therefore, is invariably an exothermic process. In other words,\mathrm{\Delta \mathrm{H}} of adsorption is always negative.

The amount of gas adsorbed by a solid depends on the nature of gas. In general, easily liquefiable gases (i.e., with higher critical temperatures) are readily adsorbed as van der waals' forces are stronger near the critical temperatures.

Physical adsorption of gas is generally reversible.
Solid+Gas \rightleftharpoons Gas/Solid+Heat

In adsorption, more of the gas is adsorbed when pressure is increased as the volume of the gas decreases (By Le-Chateliers's principle).

Also, the gas can be desorbed/ removed from the surface by decreasing pressure.

Since the adsorption process is exothermic, with increase in temperature, the rate of desorption increases. Hence, high temperature is not favourable for physical adsorption.

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jitender.kumar

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