Question

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

• 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

Answer 1

The correct option is B The adsorption is accompanied by a decreases in enthalpy

Physical adsorption takes place with the 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.