Question

Methylene blue, from its aqueous solution, is absorbed on activated charcoal ${25}^{\circ }C$. For this process, the correct statement is

• A. the absorption requires activation at ${25}^{\circ }C$
• B. the absorption is accompained by a decreases in enthalpy
• C. the absorption increases with increase of temperature
• D. the absorption is irreversible.

Answer 1

The correct option is B the absorption is accompained by a decreases in enthalpy

Physical absorption takes place with decrease in enthalpy thus exothermic change. It is physical absorption and does not require activation. Thus, (a) is correct.
Being physical absorption $\Delta H<0$ thus, (b) is correct. Exothermic reaction is favoured at low temperature thus (c) is incorrect. Physical absorption is always reversible, thus (d) is incorrect.