Question

Comment on the following statements : (a) An exothermic reaction is always thermodynamically spontaneous. (b) The entropy of a substance increases in going from the liquid to the vapour state at any temperature. (c) Reaction with ΔG° < 0 always have an equilibrium constant greater than 1.

Answer 1

"(a) An exothermic reaction is not always spontaneous because if $\Delta s$ is negative and $T\Delta S>\Delta H$ in magnitude then according to the equation $\Delta G\quad =\quad \Delta H\quad -\quad T\Delta S$, $\Delta G$ will be positive and then process will be non-spontaneous.

(b) At any temperature, the molecules in the vapour state have greater freedom of moion becasue of lesser intermolecular forces of attraction than in the liquid state.

(c) $-\Delta { G }^{ o }\quad =\quad -RTlnK$, thus, If $\Delta { G }^{ o }$ is less than zero, it is -ve, then lnK will be +ve and K will be greater than 1."