Question

Which equation represents Freundlich adsorption isotherm (physical adsorption is basis of this theory) ?

• A. $\frac{ x }{ m }= K ( P )^{1 / n }$ where $x$ is amount of gas adsorbed on mass ' $m$ ' at pressure $P$
• B. $\log \frac{x}{m}=\log K+\frac{1}{n} \log P$
• C. $\frac{x}{m}=KP$ at low pressure and $\frac{x}{ m}=K$ at high pressure
• D. All of these

Answer 1

Answer: (D)

The equation $\frac{ x }{ m }= K ( P )^{1 / n }$ represents Freundlich adsorption isotherm.It is an empirical relationship where $x$ is the mass of the gas adsorbed on mass $m$ of the adsorbent at pressure $P . K$ and $n$ are constants that depend on the nature of the adsorbent and the gas at a particular temperature.
Freundlich isotherm only approximately explains the behaviour of adsorption. The value of $1 / n$ can be between 0 to 1 , therefore the equation holds good only over a limited range of pressure.
At high pressure when $1 / n =0, \frac{ x }{ m }= K$, i.e. the adsorption is independent of pressure.
At low pressure when $1 / n =1, \frac{ x }{ m }= k$ P, i.e. the adsorption is directly proportional to pressure.
If we take log to the Freundlich isotherm $\frac{ x }{ m }= K ( P )^{1 / n }$ then we get following equation-
$\log \frac{x}{m}=\log K+\frac{1}{n} \log P$