Question

Which among the following gases is adsorbed to greater extent at similar conditions of temperature and pressure if the adsorbent remains same?

• A. $\text{N}_2$
• B. $\text{Cl}_2$
• C. $\text{H}_2$
• D. $\text{O}_2$

Hint:

To quickly rank the physical adsorption of non-polar gases, simply look at their molecular weight!
Higher Molecular Weight $\rightarrow$ Stronger van der Waals Forces $\rightarrow$ Higher Critical Temperature $\rightarrow$ Easier Liquefaction $\rightarrow$ Greater Adsorption.
Since $\text{Cl}_2$ ($71\text{ g/mol}$) is by far the heaviest among the choices, it wins instantly.

Answer 1

The Correct Option is B

Step 1: Understanding the Question:
The question asks to identify which of the given gases ($\text{N}_2$, $\text{Cl}_2$, $\text{H}_2$, or $\text{O}_2$) will undergo the maximum extent of physisorption on a given solid adsorbent under identical conditions of temperature and pressure.

Step 2: Key Formula or Approach:
Physical adsorption (physisorption) is non-specific and depends directly on the nature of the gas being adsorbed.
The extent of physisorption of a gas on a solid surface is directly proportional to the ease of liquefaction of that gas.
The ease of liquefaction is determined by its critical temperature ($T_c$). A gas with a higher critical temperature has stronger intermolecular van der Waals forces of attraction, allowing it to be adsorbed more readily.

Step 3: Detailed Explanation:
Let's evaluate the intermolecular forces present in each option: $\text{H}_2$, $\text{N}_2$, $\text{O}_2$, and $\text{Cl}_2$.
All four are non-polar diatomic molecules, meaning their main intermolecular interactions are London dispersion forces.
The strength of London dispersion forces increases with the size and molecular mass of the chemical species because larger electron clouds are more easily polarizable.
Let's compare their molecular masses:
$\text{H}_2 \approx 2\text{ g/mol}$
$\text{N}_2 \approx 28\text{ g/mol}$
$\text{O}_2 \approx 32\text{ g/mol}$
$\text{Cl}_2 \approx 71\text{ g/mol}$
Chlorine ($\text{Cl}_2$) has the highest molecular mass and largest electron cloud, resulting in the strongest intermolecular forces of attraction among the choices.
Consequently, $\text{Cl}_2$ has the highest critical temperature and is the most easily liquefiable gas.
Because it liquefies easily, its molecules interact much more strongly with the surface of the adsorbent, resulting in a significantly greater extent of adsorption compared to $\text{N}_2$, $\text{H}_2$, and $\text{O}_2$.

Step 4: Final Answer:
$\text{Cl}_2$ is adsorbed to the greatest extent because it is the most easily liquefiable gas, matching option (B).