Question

Which one is not correct according to Langmuir adsorption isotherm at very high pressure?

• A. It is valid for chemisorption.
• B. $\frac{x}{m}=\frac{a}{b}$
• C. $ln\frac{x}{m}=-\frac{\Delta H^o}{RT}+\frac{\Delta S^o}{R}$
• D. At very high pressure rate of adsorption > rate of desorption

Answer 1

The correct option is C $ln\frac{x}{m}=-\frac{\Delta H^o}{RT}+\frac{\Delta S^o}{R}$

Langmuir adsorption isotherm is applicable for chemisorption.
If Langmuir adsorption isotherm is expressed as:

$\frac{x}{m}=\frac{aP}{1+bP}$

At very high pressure, $1+bP=bP$

therefore, $\frac{x}{m}=\frac{aP}{bP}=\frac{a}{b}$

High pressure is favourable for adsorption and low pressure is favourable for desorption process. At very high pressure rate of adsorption > rate of desorption.
Option C doesn't represent the Langmuir adsorption model.

Hence, option C is the answer.