Chapter 6, Problem 6.14DQ

Interpretation Introduction

Interpretation:

Assumptions that are used to derive the Langmuir isotherm have to be explained and justified.

Concept introduction:

Adsorption isotherms:

It is defined as the change of the fractional coverage of the surface with pressure at a selected temperature.

Langmuir isotherm:

It is based on mainly three assumptions which are given below:

• Beyond monolayer coverage, adsorption won’t proceed.
• In this theory, all the molecular sites are considered to be equivalent.
• The interactions between adsorbed molecules are absent.

The mathematical expression of the Langmuir isotherm is given as,

  $\begin{array}{l}\text{θ}\text{=}\frac{\text{αp}}{\text{1+αp}}\text{;}\text{α}\text{=}\frac{{\text{k}}_{\text{a}}}{{\text{k}}_{\text{d}}}\\ \\ {\text{k}}_{\text{a}}\text{-}\text{Rate}\text{constant}\text{for}\text{adsorption}\\ {\text{k}}_{\text{d}}\text{-}\text{Rate}\text{constant}\text{for}\text{desorption}\\ \text{θ}\text{-}\text{Fractional}\text{coverage}\\ \text{p}\text{-}\text{Partial}\text{pressure}\end{array}$