When we plot a graph between the extent of adsorption Vs, pressure at constant temperature, it is called adsorption isotherm. Freundlich isotherm fails at high pressure of gas whereas Langmuir adsorption isotherm does not.
Langmuir adsorption isotherm is based on kinetic theory of gases. It involves two processes, i.e., adsorption and desorption. It is applicable to chemical adsorption in which unimolecular layer is formed.
Freundlich adsorption isotherm is based on assumption that every adsorption site is equivalent. It is applicable to physical adsorption.
