Question

In view of the signs of ${\Delta }_{r}G°$ for the following reactions
$Pb{O}_2+Pb\to 2PbO,{\Delta }_r{G}^{\circ }<0$
$Sn{O}_2+Sn\to 2SnO,{\Delta }_r{G}^{\circ }>0$
Which oxidation states are more characteristic for lead and tin?

• A. For lead +4, for tin +2
• B. For lead +2, for tin +2
• C. For lead +4, for tin +4
• D. For lead +2, for tin +4

Answer 1

Answer: (D)

Since$\Delta G^{\circ }<0$ i.e., it is negative. Therefore, the reaction is spontaneous in the forward direction. This suggest that $P{b}^{2+}$ is more stable than $P{b}^{4+}$

Since $\Delta G^{\circ }>0$ i.e., it is positive, therefore, the reaction is non-spontaneous in the forward direction. But it will be spontaneous in the backward direction. This suggests that $S{n}^{2+}$. These facts are also supported by the inert pair effect down the group.