Question

During adsorption, enthalpy and entropy of the system are _________ but $\Delta G$ must be __________.

• A. negative, positive
• B. negative, negative
• C. positive, negative
• D. positive, positive

Answer 1

The correct option is B negative, negative

During adsorption, enthalpy and entropy of the system are negative but $\Delta G$ must be negative so that the process is spontaneous. Adsorption is accompanied by decrease in the free energy of the system as it is a spontaneous process. When $\Delta G$ becomes zero, adsorption equilibrium is established. Since it is an exothermic process, $\Delta H$ is negative. Since the adhering of gas molecules to the surface lowers the randomness, the $\Delta S$ is negative.