Chemical and Ionic Equilibrium - Result Question 1

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) $\Delta G^{\circ} < 0, K < 1$

{{ < details"Show Answer" >}}

Answer:

Correct Answer: 1. (d)

Solution:

1. 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 $e^{-\Delta G^{\circ} / R T} < 1$ 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.

{{ < /details >}}