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.
At high pressure, x/m becomes independent of the values of P.
In this range of pressure ,
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:
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