JAMB Chemistry 2024 Paper

Concept:Spontaneity is decided by the Gibbs free energy change, not by enthalpy alone.Explanation:At constant temperature and pressure, the Gibbs free energy change is$$\Delta G = \Delta H - T\Delta S$$A reaction is spontaneous only when $\Delta G < 0$.A negative enthalpy change, $\Delta H < 0$, is favourable, but it alone does not guarantee spontaneity because the entropy term $-T\Delta S$ may make $\Delta G$ positive.Option B says $\Delta G > 1$, meaning $\Delta G$ is positive, so that reaction would not be spontaneous.An entropy change of zero, $\Delta S = 0$, or equality between $\Delta H$ and $\Delta G$, does not ensure a negative $\Delta G$.The true requirement is a negative free energy change.Answer:A typical chemical reaction is spontaneous if the free energy change is negative, that is $\Delta G < 0$.