Question

Sketch a set of Langmuir Isotherms and provide their formula.

Answer 1

Langmuir adsorption isotherm is only a uni-molecular layer adsorption takesw place on the surface.

The adsorbed layer is uniform all over the adsorbent.

There is no interaction between adsorbed molecules.

There is an equilibrium between the adsorption and desorption from the surface of the adsorbent.

Langmuir adsorption isotherm is   w=AP/1+BP

where A&B are constants,w is the mass of gas adsorbed by unit mass of the adsorbent and P is the pressure of the gas.

At low pressure, P is small. therefore 1+BP=1 . the equqtion becomes w=AP

A graph of w should be straight line passing through the origin.

At high pressure, P is large.Therfore 1+BP=BP.The equation becomes w=AP/BP . this means the amount of gas adsorbed remains constant at high pressure.

When the surface of the adsorbent is completely covered by the adsorbate molecules,the amount of gas adsorbed reaches a limiting value.

Langmuir adsorption isotherm is able to explain the adsorption behavior at both high and low pressures.