Question

The correct statements regarding the adsorption of a gas on a solid surface is/are:

• A. Adsorption is always exothermic
• B. Physisorption may transform to chemisorption at high temperatures
• C. Adsorption is a non-spontaneous process
• D. Chemisorption is more exothermic than physisorption, however it is slow because it requires a higher energy of activation

Answer 1

Answer: (A), (B), (D)

The correct options are
A Adsorption is always exothermic
B Physisorption may transform to chemisorption at high temperatures
D Chemisorption is more exothermic than physisorption, however it is slow because it requires a higher energy of activation

• Adsorption is a spontaneous process as it occurs without any external support. In adsorption, free gas molecules gets adsorbed on the surface and hence, the entropy is decreased, so to compensate the decrease in entropy, the enthalpy of adsorption must be negative.
• Physisorption may turn into chemisorption at higher temperatures when there is chance of bond formation and when the temperature is enough to provide the activation energy.
• Physisorption is a result of van der Waal's interaction hence it will release lesser energy than chemisorption