Shapes of different equilibrium adsorption isotherms

Shapes of different equilibrium adsorption isotherms 8.1.1 The Linear Isotherm 

The simplest isotherm is the linear isotherm. At very low concentrations the molecules adsorbed are widely spaced over the adsorbent surface so that one molecule has no influence on another. For these conditions an isotherm similar to Henry s law 

This is the most commonly used isotherm. This adsorption assumes that at higher concentration the rate of adsorption decreases because of lack of space on the adsorbent surface. Therefore, the adsorption is proportional to concentration as well as empty surface available and rate of desorption is proportional to the surface area occupied by adsorbate. The general form of this isotherm is given below 

This isotherm can also be expressed in terms of partial pressure of adsorbate in the gas phase P or relative pressure PjP where is the saturated vapor pressure. 

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