Question

According to langmuir adsorption isotherm:
For adsorption of a gas over solid surface, rate of adsorption is proportional to:

• A. Fraction of surface available for adsorption.
• B. Pressure of gas
• C. Both (a) and (b)
• D. Fraction of surface covered on adsorbent.

Answer 1

The correct option is C Both (a) and (b)

In Langmuir adsorption isotherm,
$\Theta$ : Fraction of surface covered on adsorbent
$1-\Theta$ : Free surface are
$P$ : Pressure of gas
By langmuir adsorption isotherm,
$\text{Rate of adsorption}\propto \text{Fraction of surface available for adsorption}$​
$\text{Rate of adsorption}\propto \text{Pressure of gas}$
$\therefore$
$\text{Rate of adsorption}\propto P(1-\Theta )$
$\text{Rate of adsorption}=k_{a}P(1-\Theta )$

$\text{Rate of dessorption}\propto \text{Fraction of surface covered on adsorbent}$​
$\text{Rate of desorption}\propto \Theta$
$\text{Rate of desorption}=k_d\Theta$
$k_a$ and $k_d$ are rate constants.

At equilibrium condition,
$\text{Rate of adsorption}=\text{Rate of desorption}$