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

Options

  1. AThe adsorption requires activation at 25 o C.
  2. BThe adsorption is accompanied by a decrease in enthalpy
  3. CThe adsorption increases with increase of temperature.
  4. DThe adsorption is irreversible.

Correct answer

B. The adsorption is accompanied by a decrease in enthalpy

Step-by-step solution

It is the process of Physical adsorption as charcoal is already activated. Since physical adsorption is spontaneous Δ G is -ve Δ G = Δ H - T Δ S as Δ S is -ve (passage of methylene blue from aqueous phase over the surface of adsorbent) i.e. Δ H is highly -ve since process is exothermic in nature. Physical adsorption is reversible in nature. Physical adsorption decreases with increase in temperature.

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