What is an adsorption isotherm? Describe Freundlich adsorption isotherm.

Explanation

A plot between the amount of gas adsorbed per gram of adsorbent `(x//m)` and the pressure of the adsorbate at constant temperature is called adsorption isotherm.
Freundlich adsoption isother
`(x)/(m)=KP^(1//n) (` at moderate pressure `) ….(i)`
where `x` is the amount of gas adsorbed by `m` gram of the adsorbent at a pressure `P`, while `K` and `n` are constants.

Taking logarithm of `Eq. (i)` we get
`log``(x)/(m)=(1)/(n)logP+logK`
As the plot of `logx//m` versus `logP` is a straight line, the Freundlich adsoption is valide. This isotherm explains the behaviour of adsorption approximately and `1//n` can have any value between 0 and 1 .
`a.` when `1//n(` slope `)=0 , x//m=` constant which shows that adsorption is independent of pressure.
`b.` when `1//n=1,x//m=KP,i.e., x//m prop P` , the adsoption varies directly as per pressure. Both these condictions are experimentally varified, however, the experimental isotherm always sums up to approach saturation at high pressure. This cannot be explained at Freundlich adsoption isotherm.