Surface Chemistry - Result Question 19
20. Methylene blue, from its aqueous solution, is adsorbed on activated charcoal at $25^{\circ} C$. For this process, the correct statement is
(2013 Adv.)
(a) the adsorption requires activation at $25^{\circ} C$
(b) the adsorption is accompanied by a decreases in enthalpy
(c) the adsorption increases with increase of temperature
(d) the adsorption is irreversible
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Answer:
Correct Answer: 20. (b)
Solution:
Physical adsorption takes place with decrease in enthalpy thus exothermic change. It is physical adsorption and does not require activation. Thus, $(a)$ is incorrect.
Being physical adsorption $\Delta H<0$ thus, $(b)$ is correct. Exothermic reaction is favoured at low temperature thus (c) is incorrect. Physical adsorption is always reversible, thus (d) is incorrect.
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