Question

A gas undergoes physical adsorption on a surface and follows the given Freundlich adsorption isotherm equation; $\dfrac{x}{m}=K{{p}^{0.5}}$
Adsorption of the gas increases with:
A. decrease in p and decrease in T
B. increase in p and increase in T
C. increase in p and decrease in T
D. decrease in p and increase in T

Answer 1

. Adsorption is the process by which molecules of a substance for example a gas or a liquid collect on the surface of another substance like solid. In this process, the molecules are attracted to the surface but do not enter in the solids minute spaces.

Complete step by step answer:
Adsorption isotherm is shown by a curve which expresses the variation in the amount of gas adsorbed by the adsorbent with pressure at constant temperature.
Freundlich adsorption isotherm provides an empirical relationship between the amount of gas adsorbed by a unit mass of solid adsorbent and pressure at a particular temperature. It can be expressed by the following equation:
$\dfrac{x}{m}=K{{p}^{\dfrac{1}{n}}}(n>1)$

Where, x represents the mass of the gas adsorbed, m mass of the adsorbent, p represents pressure. k and n are constants that depend on the nature of the adsorbent and the gas at a particular temperature.
The mass of the gas adsorbed per gram of the adsorbent is plotted against pressure in the form of a curve to show their relationship. At a fixed pressure physical adsorption decreases with increase in temperature. The curve reaches a saturation point at high pressure.
So, the correct answer is “Option C”.

Note: There is a main disadvantage of freundlich isotherm that it only approximately explains the behavior of adsorption not properly. The value of $\dfrac{1}{n}$ can be between 0 and 1, therefore the equation holds good only over a limited range of pressure.