Discuss the effect of pressure and temperature on the adsorption of gases on solids. 

Answer:

Effect of pressure on adsorption. The extent of adsorption of a gas per unit mass of adsorbent (x / m) increases with increase of pressure at a constant temperature.
(i) For a lower range of pressure (x / m) is directly proportional to the applied pressure. Larger the pressure more is the amount of gas adsorbed, lower the pressure small is the amount of a gas adsorbed. That is
$\frac{\mathrm{x}}{\mathrm{m}}\propto \mathrm{p}$ (as a constant temperature)

(ii) For a high pressure range the extent of adsorption of a gas per unit mass of the adsorbent (x / m) is independent of the applied pressure. That is

(iii) For a moderate pressure range the value of x/m is proportional to a Fractional power of pressure. That is
$\frac{\mathrm{x}}{\mathrm{m}}\propto {\mathrm{p}}^{1/\mathrm{n}}$ (where T is constant)            
where 1 / n is a fraction. Its value may be between 0 and 1. Fig. (a) and (b) show the variations of the extent of adsorption of a gas on an adsorbent as predicted by Frundlich equations (i) and (ii) respectively.
                $\frac{\mathrm{x}}{\mathrm{m}}= \mathrm{k} {\mathrm{p}}^{1/\mathrm{n}}$                                 ...(i)

and $\log \left(\frac{\mathrm{x}}{\mathrm{m}}\right) = \log \mathrm{k} + \frac{1}{\mathrm{n}}\log \mathrm{p}$                ...(ii)

Effect of temperature on adsorption: The amount of a gas adsorbed per unit mass of a solid surface (x / m) decreases with increase of temperature in case of physical adsorption. However, in case of chemical adsorption as the temperature increases x / m increases, attains a maximum value then decreases.