MHT CET202613 April 2026Morning ShiftChemistrySurface ChemistryActual
Which of the following statements is correct for the spontaneous adsorption of a gas?
Options
- AS is negative and, therefore H should be highly positive
- BS is negative and therefore, H should be highly negative.
- CS is positive and therefore, H should be negative.
- DS is positive and therefore, H should also be highly positive.
Correct answer
B. S is negative and therefore, H should be highly negative.
Step-by-step solution
During the adsorption of a gas, the gas molecules are restricted to the surface of the solid, which decreases their randomness or entropy. Thus, the change in entropy, S , is negative. For a process to be spontaneous, the change in Gibbs free energy, G , must be negative. According to the Gibbs-Helmholtz equation: G = H - T S Since S is negative, the term -T S becomes positive. For G to be negative, the enthalpy change, H , must be negative and its magnitude must be large enough to overcome the positive -T S term.