Question

Why both Freundlich and Langmuir adsorption isotherms hold good at high pressure and fail at low pressure?

Answer 1

Experimentally, it was determined that the extent of gas adsorption varies directly with pressure. It directly varies with pressure raised to the power 1/n until saturation pressure P_s is reached. Beyond that point, the rate of adsorption saturates even after applying higher pressure. Thus, the Freundlich adsorption isotherm fails at higher pressure.