NEET Chemistry Surface Chemistry Questions Solved


What is an adsorption isotherm? Describe Freundlich adsorption isotherm. 

Adsorption isotherm: A graph between the amount of the gas adsorbed 

per gram of the adsorbent (x/m) and the equlibrium pressure of the adsorbate

at constant temperature is called the adsorption isotherm.

The extent of adsorption is usually expressed as x/m,


Variation of x/m with increase in pressure at constant temperature 

                   (Freundlich adsorption isotherm)

A relationship between the amount adsorbed (x/m) and the equilibrium 

pressure (P) can be obtained as follows:

At low values of P, the graph is nearly straight and sloping.

xmP          or xm=constant×P1

At high pressure, x/m becomes independent of the values of P. 

In this range of pressure ,

xmP°          or xm=constant×P°

In the intermediate range of pressure, x/m will depend on P raised to

powers between 1 and 0 i.e. fraction. For a small range of pressure values,

we can write:

xmP1/n      or  xm=kP1/n


[n=Positive integer

 k=constant depends upon the nature of 

     adsorbate and adsorbent at a particular temperature.

The factor 1/n has values between 0 and1.]

This relationship was given by Freundlich and is known as Freundlich adsorption 




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