Which of the following conditions can be used to change physical adsorption of a gas to chemical adsorption?

Increase in temperature

The correct answer is option 2:  Increase in temperature.

Let us look at why this is correct

Physical adsorption:

• Occurs due to weak intermolecular forces like Van der Waals forces between the gas molecules and the adsorbent surface.
• Happens readily at low temperatures as the kinetic energy of the gas molecules is low, allowing them to stay closer to the surface for longer.
• Forms multilayer adsorption, where multiple layers of gas molecules can stack on top of each other.
• Is easily reversible, meaning the adsorbed molecules can readily desorb (leave the surface) with a small increase in temperature or decrease in pressure.

Chemical adsorption:

• Involves the formation of chemical bonds between the gas molecules and the adsorbent surface.
• Requires higher activation energy to overcome the potential energy barrier for bond formation, which is why it typically occurs at higher temperatures.
• Forms monolayer adsorption, where only a single layer of gas molecules directly bonds to the surface.
• Is generally irreversible or difficult to reverse due to the strong chemical bonds involved.

Therefore, increasing the temperature provides enough energy for the gas molecules to overcome the energy barrier and form chemical bonds with the adsorbent surface, leading to a transition from physical to chemical adsorption.

Here's a table summarizing the key differences between physical and chemical adsorption:

The other options have the opposite effect or are not relevant:

(A) Decrease in temperature: This would further favor physical adsorption and make it less likely for chemical adsorption to occur.

(C) Using catalyst: Catalysts can accelerate the rate of both physical and chemical adsorption, but they don't fundamentally change the type of adsorption.

(D) Increasing surface area of adsorbent: This will increase the amount of both physical and chemical adsorption that can occur, but it won't change the type of adsorption itself.