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

Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at 25o C. For this process, the correct statement is 
  1. The adsorption requires activation at 25oC.
  2. The adsorption is accompanied by a decrease in enthalpy
  3. The adsorption increases with increase of temperature.
  4. The adsorption is irreversible.

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.

Asked in: JEE Advanced 2013 (Paper 1)

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