Question

Choose the correct option(s) regarding adsorption isobars for chemisorption and physisorption:

• A. As the temperature decreases , physical adsorption decreases continuously.
• B. As the temperature increases, physical adsorption decreases.
• C. For chemisorption isobar, as the temperature increases there is an increase in the chemisorption initially because activation energy is required to initiate the process.
• D. For chemisorption isobar, as the temperature increases there is decrease in the chemisorption initially because there is a decrease in gibbs free energy

Answer 1

Answer: (B), (C)

For chemisorption isobar, as the temperature increases there is an increase in the chemisorption initially because activation energy is required to initiate the process.

Adsorption Isobar
The variation in the amount of gas adsorbed by the adsorbent with temperature at constant pressure. It can be expressed by a curve termed as adsorption isobar.

At constant pressure P,

$x$ is the mass of the gas adsorbed.
$m$ is the mass of adsorbent.
$\left(\frac{x}{m}\right)$ is extent of adsorption per unit mass of adsorbent
For chemisorption,
As the temperature increases, chemical adsorption increases initially, reaches a maximum, then decreases continuously.
The curve obtained is:
There is an increase in the chemisorption initially because activation energy is required .Thus, chemical adsorption is also known as “activated adsorption”.


For physisorption
With increase in temperature, physical adsorption decreases continuously
Hence the curve obtained is: