Question

Langmuir isotherm equation is based on which of the following theories?
A) Collision theory
B) Kinetic theory of gases
C) Thermodynamics
D) Wave mechanic theory

Answer 1

Hint:We know that adsorption is a process in which molecules get deposited on the surface. Adsorption takes place at a constant temperature but varying pressure is called adsorption isotherm. It is of two types that are Langmuir adsorption isotherm and Freundlich isotherm.


Complete solution:
We all know about adsorption. It is a process in which molecules get deposited on the surface. The surface on which adsorption occurs is called adsorbent and the molecules that are getting absorbed are called adsorbate. Adsorption takes place at a constant temperature but varying pressure is called adsorption isotherm. Langmuir isotherm equation describes the equilibrium between adsorbate and adsorbent. It assumes that adsorbate behaves like an ideal gas at isothermal conditions. It is based on the kinetic theory of gases. Langmuir expression is given as
$\dfrac{x}{m} = \dfrac{{ap}}{{1 + bp}}$
$m = $ Mass of adsorbent
$x = $ Mass adsorbed
$a,b = $ Langmuir parameters
$p = $ Pressure
This equation is valid only below the critical desorption pressure. Langmuir assumed that the adsorption consists of two opposing forces. The two opposing forces are
$\left( i \right)$ Adsorption of gas molecules on the surface of the solid
$\left( {ii} \right)$ Desorption of the adsorbed gas molecules from the surface of the solid.
According to this model, adsorption and desorption are reversible processes. The adsorbent surface is assumed to have several interaction sites for adsorption.

Thus, the correct option is (B).


Note:Langmuir isotherm equation has certain limitations. It is valid only at low pressure and high temperature. The adsorption is stopped when the adsorbent is fully covered but there is an equilibrium between adsorption and desorption.