Write equilibrium constant expressions for these heterogeneous equilibria.
\begin{equation}
\begin{array}{l}{\text { a. } 2 \mathrm{NaHCO}_{3}(\mathrm{s}) \rightleftharpoons \mathrm{Na}_{2} \mathrm{CO}_{3}(\mathrm{s})+\mathrm{H}_{2} \mathrm{O}(\mathrm{g})+\mathrm{CO}_{2}(\mathrm{g})} \\ {\text { b. } \mathrm{C}_{6} \mathrm{H}_{6}(1) \rightleftharpoons \mathrm{C}_{6} \mathrm{H}_{6}(\mathrm{g})}\end{array}
\end{equation}