# Freundlich Adsorption Isotherm

According to him:

(i)   At low pressure:

At low pressure the graph is almost

Straight. i.e. $\dfrac{x}{m}\propto p$

$\dfrac{x}{m} = KP$

Where, K = constant

(ii)  At high pressure:

x / m becomes almost constant and does not change with pressure

$\dfrac{x}{m} \propto P^0$

$or\hspace{3mm} \dfrac{x}{m} = KP^0$

(iii)   At intermediate value of pressure.

Here,

$\dfrac{x}{m} \propto P^{1/n}$

$\dfrac{x}{m} = KP^{1/n}$ …..(1)

Here ‘n’ is a constant depending upon nature of adsorbate and adsorbent.

The value of K, n can be determined as follows: On taking logarithm of equation (1) we get

$\log_e \dfrac{x}{m} = \log_Ek + \dfrac{1}{n} \log_e P$

Thus, on plotting a graph between x/ m and logep a straight line is obtained.

Here,

$\text{slope} = \dfrac{1}{n} \\[3mm] \text{Intercept} = \log_e K$