Question

Which of the following statement(s) is/are true regarding Freundlich adsorption isotherm?

• A. It holds good for a limited range of pressure of the gas, but generally, fails at high pressure.
• B. At low pressure, the extent of adsorption linearly dependent
  on pressure.
• C. The extent of adsorption will attain a saturation point at high pressure.
• D. All of the above.

Answer 1

The correct option is D All of the above.

By Freundlich Adsorption Isotherm,
$\frac{x}{m}\propto p^{\frac{1}{n}}$
n > 1
$\frac{x}{m}$ is the extent of adsorption which means the amount of gas adsorbed by the adsorbent with pressure at constant temperature.
$\frac{x}{m}=k{p}^{\frac{1}{n}}....\left(1\right)$
k and n are constants that depends on the nature of gas and adsorbent.
Taking log of equation (1) gives,

log $\left(\frac{x}{m}\right)=logk+\frac{1}{n}logP$

Here, the factor $\frac{1}{n}$ can have value between 0 to 1 based on the pressure range.

Freundlich isotherm holds good over a limited range of low pressure.
Hence, at low temperature, the isotherm is a straight line
$\therefore \frac{1}{n}=1$

$\Rightarrow \frac{x}{m}=kp$
Thus, the extent of adsorption linearly dependent on pressure.

At intermediate pressure,
$0<\frac{1}{n}<1$
Hence,
$\Rightarrow \frac{x}{m}=k{p}^{\frac{1}{n}}$
Thus, the extent of adsorption dependent on power of pressure.


At high pressure, the extent of adsorption attains a constant value and becomes independent of pressure.
Thus, $\frac{1}{n}=0$
$\Rightarrow \frac{x}{m}=k{p}^0$
$\Rightarrow \frac{x}{m}=k$
Thus, extent of adsorption attains a saturation point.