Chemical and Ionic Equilibrium - Result Question 57
####1. The incorrect match in the following is (2019 Main, 12 April II)
(a) $\Delta G^{\circ}<0, K>1$
(b) $\Delta G^{\circ}=0, K=1$
(c) $\Delta G^{\circ}>0, K<1$
(d) $\Delta G^{\circ}<0, K<1$
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Answer:
Correct Answer: 1. (d)
Solution:
- The incorrect match is $\Delta G^{\circ}<0, K<1$.
For an ideal gas $\Delta G^{\circ}=-R T \ln K$.
$\therefore \quad \ln K=-\frac{\Delta G^{\circ}}{R T}$ and $K=e^{-\Delta G^{\circ} / R T}$
The above equation is helpful in predicting the spontaneity of the reaction. e.g.
(i) If $\Delta G^{\circ}<0,-\Delta G^{\circ} / R T=+$ ve and $e^{-\Delta G^{\circ} / R T}>1$ and hence, $K>1$. It means that the reaction occur spontaneously in the forward direction or products predominate over reactants.
(ii) If $\Delta G^{\circ}>0 ;-\Delta G^{\circ} / R T=-$ ve and $e^{-\Delta G^{%} R T}<1$ and hence, $K<1$. It means that the reaction is non-spontaneous in forward direction (i.e. product side) but spontaneous in reverse direction (i.e. reactants predominate over products or the reaction occurs rarely).
(iii) When $K=1$, then $\Delta G^{\circ}=0$. This situation generally occur at equilibrium.
