Question

The correct statements about the adsorption of gas on solid adsorbent are: 
Adsorption is always exothermic. Physisorption may transform into chemisorption at high temperature. Physisorption increases with increasing temperature but chemisorption decreases with increasing temperature. In physisorption enthalpy of adsorption is 100 kJ mol\(^{-1}\). 
 

• A. II & IV only
• B. III & IV only
• C. II & III only
• D. I & II only

Hint:

Remember the key differences between physisorption and chemisorption, including their enthalpy changes and temperature dependence.

Answer 1

The Correct Option is D

1. Adsorption is always exothermic:

Adsorption is a process where gas molecules adhere to a solid surface. This process releases energy, making it exothermic.
Statement I is correct.

2. Physisorption may transform into chemisorption at high temperature:

Physisorption involves weak van der Waals forces. At high temperatures, these forces can be overcome, and chemical bonds may form, leading to chemisorption.
Statement II is correct.

3. Physisorption increases with increasing temperature but chemisorption decreases with increasing temperature:

Physisorption decreases with increasing temperature because the kinetic energy of the gas molecules increases, making it harder for them to adhere to the surface.
Chemisorption also decreases with increasing temperature after reaching an optimum temperature, as the activation energy required for bond formation is supplied.
Statement III is incorrect.

4. In physisorption enthalpy of adsorption is 100 kJ mol\(^{-1}\):

The enthalpy of adsorption for physisorption is typically in the range of 20-40 kJ mol\(^{-1}\), not 100 kJ mol\(^{-1}\).
Statement IV is incorrect.

Therefore, the correct statements are I and II.

Final Answer:
I & II only.