JEE Advanced 2022 Paper 1 Q10 Chemistry Physical Chemistry States of Matter Medium

JEE Advanced 2022 Paper 1 · Q10 · States of Matter

The correct option(s) related to adsorption processes is(are)

  1. A. Chemisorption results in unimolecular layer
  2. B. The enthalpy change during physisorption is in the range of 100 to 140 kJ mol$^{-1}$
  3. C. Chemisorption is an endothermic process
  4. D. Lowering the temperature favors physisorption processes
JEE Advanced multi-correct — pick every correct option, then check.
Reveal answer + step-by-step solution

Correct answer:A, D

Solution

(A) TRUE. In chemisorption a chemical bond is formed between the adsorbate and the surface, so the adsorbate forms only a monolayer (further adsorbate molecules cannot form a second chemisorbed layer because the surface bonding sites are saturated).

(B) FALSE. The enthalpy change for physisorption is typically small (about 20–40 kJ mol$^{-1}$, comparable to van der Waals interactions); 100–140 kJ mol$^{-1}$ is in the range of chemisorption.

(C) FALSE. Both physisorption and chemisorption are exothermic processes — adsorption necessarily releases heat (because $\Delta S$ is negative on adsorption, $\Delta H$ must be negative for $\Delta G$ to be negative).

(D) TRUE. Physisorption is exothermic with small magnitude $|\Delta H|$, and is favoured at low temperatures. Lowering the temperature increases the extent of physisorption.

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