Question

According to Freundlich adsorption isotherm, which of the following is correct?

• A. $x/m\propto p^o$
• B. All the above are correct for different ranges of pressure.
• C. $x/m\propto p^1$
• D. $x/m\propto p^{1/n}$

Answer 1

Answer: (B)

According to Freundlich adsorption isotherm, $\frac{x}{m}=K{P}^{\frac{1}{n}}$

Where, $\frac{x}{m}=$amount of gas adsorbed per unit mass of the adsorbent at pressure $P$. $K$ and $n$ are constants, depends on the nature of the gas & nature of adsorbent.

$(n>1)$

At low pressure, extent of adsorption is directly proportional is directly proportional to pressure.

$\therefore \frac{x}{m}\propto P^1$

At high pressure, extent of adsorprtion is independent of pressure.

$\therefore \frac{x}{m}\propto P^0$

And at intermediate value of pressure, adsorption is directly proportional to pressure raised to power $\frac{1}{n}.$

$\therefore \frac{x}{m}\propto P^{\frac{1}{n}},n>1$

Experimentally it was determined that extent of adsorption varies directly with pressure till saturation pressure is reached. Beyond that point rate of adsorption saturates.