Use data from Appendix IIB to calculate the equilibrium constants at $25^{\circ} \mathrm{C}$ for each reaction. $\Delta G_{\mathrm{f}}^{\circ}$ for $\operatorname{BrCl}(g)$ is $-1.0 \mathrm{~kJ} / \mathrm{mol}$
a. $2 \mathrm{NO}_{2}(g) \rightleftharpoons \mathrm{N}_{2} \mathrm{O}_{4}(g)$
b. $\mathrm{Br}_{2}(g)+\mathrm{Cl}_{2}(g) \rightleftharpoons 2 \operatorname{BrCl}(g)$