Question

Distinguish between freundlich adsorption isotherm and langmuir adsorption isotherm.

Answer 1

Sr. No.	Points	Freundlich adsorption isotherm	Langmuir adsorption isotherm
1.	Nature of surface	Freundlich isotherm assumes that the surface of the adsorbent is heterogeneous in nature.	Langmuir isotherm assumes that the surface of the adsorbent is homogeneous with identical sites.
2.	Number of layers	It allows the formation of multiple layers of adsorbed molecules on the surface.	It assumes that only a single layer of molecules is adsorbed (monolayer adsorption).
3.	Mathematical expression	It is represented by the equation `x/m = kP^(1//n)`, where 0 < 1/n < 10.	It is represented by the equation θ = `(KP)/(1+KP')​`, where θ is the fraction of surface covered.
4.	Validity range	This isotherm is applicable only at lower pressure ranges.	This isotherm is applicable over a wide range of pressures.
5.	Saturation point	It does not predict any definite saturation point of the surface.	It predicts a saturation point where all the active sites are fully occupied by adsorbate.
6.	Theoretical basis	It is an empirical isotherm based purely on experimental observations.	It is a theoretical isotherm derived from kinetic considerations and equilibrium conditions.