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JEE Advanced2022Paper 1CHEM-II
Q.

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

  1. A

    Chemisorption results in a unimolecular layer.

  2. B

    The enthalpy change during physisorption is in the range of 100 to 140 kJ mol.

  3. C

    Chemisorption is an endothermic process.

  4. D

    Lowering the temperature favours physisorption processes.

Solution

(A) Chemisorption involves covalent or ionic bond formation with the surface, which saturates once a monolayer is built. Correct.

(B) Physisorption involves weak van der Waals forces with enthalpies typically 20 to 40 kJ mol, not 100 to 140 kJ mol. The higher range is characteristic of chemisorption. Wrong.

(C) Adsorption is accompanied by a decrease in entropy, so for spontaneity at moderate temperatures must be negative. Chemisorption is exothermic, not endothermic. Wrong.

(D) Physisorption is exothermic and reversible; by Le Chatelier's principle, lowering the temperature shifts the equilibrium toward more adsorption. Correct.

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