Question

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

• A. The adsorption requires activation at ${25}^{\circ }\text{C}$
• B. The adsorption is accompanied by a decrease in enthalpy
• C. The adsorption increases with an increase in temperature
• D. The adsorption is irreversible

Answer 1

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

This is physisorption which is spontaneous at room temperature.
It is an exothermic process. So, $\Delta H<0$.
Exothermic reactions are favoured at low temperatures.
Physcial adsorption is always reversible.