Question

Which of the following is true concerning adsorption?

(A) $\Delta \text{G 0; }\Delta S\text{ 0; }\Delta H\text{ 0}$
(B) $\Delta \text{G 0; }\Delta S\text{ 0; }\Delta H\text{ 0}$
(C) $\Delta \text{G 0; }\Delta S\text{ 0; }\Delta H\text{ 0}$
(D) $\Delta \text{G 0; }\Delta S\text{ 0; }\Delta H\text{ 0}$

Answer 1

Hint: Adsorption is considered to be an exothermic process which is explained theoretically and verified experimentally. As the particles come closer, the randomness in general decreases. Adsorption process is a feasible process at all temperatures.

Complete step by step answer:
Adsorption is the adhesion of atoms, ions or molecules from a gas, liquid or dissolved solid to a surface called the adsorbent. This process creates a film of the adsorbate on the surface of the adsorbent.
Similar to surface tension, adsorption is also a consequence of surface energy. In a bulk material, all the bonding requirements of the atoms of the material are filled by adjacent atoms in the material.
However, atoms on the surface of the adsorbent are not wholly surrounded by other adsorbent atoms and thereby attract the adsorbate particles.
The rate of adsorption can be calculated using the formula given by Freundlich's isotherm. However, we won't be discussing it under this question.
As suggested in the hint, adsorption process released heat which means that change in enthalpy is always negative i.e. $\Delta H\text{ 0}$.
Due to adhesion during adsorption, the randomness of the molecules is reduced resulting in decrease in entropy. Hence change is entropy is negative i.e. $\Delta S\text{ 0}$.
Since the change in enthalpy and change in entropy are negative, the reaction is said to be feasible in accordance to the third law of thermodynamics:
$\Delta G\text{ = }\Delta H\text{ - }T\Delta S$
Hence change in Gibbs free energy($\Delta \text{G}$) is negative i.e. $\Delta \text{G 0}$.

Therefore, the correct answer is option (B).

Note: Adsorption and absorption are mistakenly considered to be the same process. However, absorption is a bulk phenomenon and occurs in the bulk of the material. On the other hand, adsorption is a surface phenomenon and occurs only on the surface the adsorbent substance. The process in which adsorption and absorption takes place together is called sorption.