What is an adsorption isotherm? Describe Freundlich adsorption isotherm.

Hello Student
As physical adsorption is reversible, it is accompanied by decrease in pressure. Therefore, it is expected that at a given temperature the extent of adsorption will increase with the increase of pressure of the gas.
The extent of adsorption is measured as x/m where m is the mass of adsorbent and x that of adsorbate.
If the physical adsorption is limited to unimolecular layer, the plot of x/m vs. equilibrium pressure at a constant temperature is as shown.

It is evident from the graph that at a certain pressure the adsorption reaches a maximum value i.e. the adsorption becomes saturated and the corresponding pressure is called saturation pressure (Ps). Beyond this pressure the adsorption remains constant.


Comparing the above given equation with equation of straight line
y = mx + c
we know that, if we plot log p vs log x/m, we would get a straight line with slope equal to 1/n and intercept log k.