Question

Which of the following is not a favourable condition for physical adsorption?

• A. higher critical temperature of adsorbate
• B. negative $△H$
• C. high temperature
• D. high pressure

Answer 1

The correct option is C

high temperature

Unfavourable conditions :

Physical adsorption is a process in which adsorbate gets adsorbed on the adsorbent surface by weak van der Waals’ force of attraction and is an exothermic process. On increasing temperature, the interaction between adsorbate and adsorbent becomes weak and adsorbate particles get desorbed.

Hence, option $\left(D\right)$ is correct.

Favourable conditions

• At constant temperature, the rate of adsorption increases with an increase in pressure. So, option $\left(A\right)$ is a favourable condition for adsorption.

• Adsorption is an exothermic process, so $△H$ is negative. Therefore, option $\left(B\right)$ is also favourable for adsorption.

• Higher critical temperature of adsorbate increases the rate of adsorption. So, option $\left(C\right)$ is also a true condition for adsorption.