The number of statement/s which are the characteristics of physisorption is __________
A. It is highly specific in nature
B. Enthalpy of adsorption is high
C. It decreases with increase in temperature
D. It results into unimolecular layer
E. No activation energy is needed

Solution

Chemistry ma’am · 2 steps

Physisorption runs on weak van der Waals forces, so check each statement against weak forces.

1. Nature of physisorption. In physisorption, gas molecules stick to the surface by weak van der Waals forces. No chemical bond forms, so it is not specific, releases little heat and needs no activation energy.

   Statement	Physisorption actually shows	Characteristic?
   A. Highly specific	Not specific: any gas can adsorb on any surface	No (that is chemisorption)
   B. High enthalpy of adsorption	Low, about 20 to 40 kJ mol⁻¹	No (that is chemisorption)
   C. Decreases as temperature rises	Adsorption is exothermic, so by Le Chatelier it falls on heating	Yes
   D. Unimolecular layer	Multimolecular layers, because weak forces act layer on layer	No (that is chemisorption)
   E. No activation energy	No bond breaking or forming, so no energy barrier	Yes

2. So. Only statements C and E describe physisorption. A, B and D all describe chemisorption. The count is 2.

The idea to keep. Weak forces explain all of physisorption: not specific, low enthalpy, many layers, no activation energy, and less adsorption at higher temperature. Chemisorption is the opposite on each point.

Answer from the NTA final answer key. Solution by PrepWiser.