JEE Advanced 2013 Chemistry question

Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at 25 °C. For this process, the correct statement is

(A)The adsorption requires activation at 25 °C.
(B)The adsorption is accompanied by a decrease in enthalpy.Correct
(C)The adsorption increases with increase of temperature.
(D)The adsorption is irreversible.

Answer: (B)

Solution

Adsorption of methylene blue on charcoal is physical adsorption. Adsorption is spontaneous (ΔG < 0) and the adsorbed molecules lose freedom (ΔS < 0), so ΔH must be negative: it is

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Question ID VK-026146