Question

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

• A. As the temperature decreases , physical adsorption decreases continuously.
• B. None of the above
• C. For chemisorption isobar, as the temperature increases there is decrease in the chemisorption initially because there is a decrease in gibbs free energy
• D. As the temperature increases, physical adsorption decreases.

Answer 1

The correct option is D As the temperature increases, physical adsorption decreases.

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: