The given chemical reaction is:
[COCl_2(g) \rightleftharpoons CO(g) + Cl_2(g) \quad K = 1.5 \times 10^{10}]
We need to write the expression for the equilibrium constant ((K)) for this reaction.
The equilibrium constant (K) expression for the given reaction is:
\[ K = \frac{[CO][Cl_2]}{[COCl_2]} \]
where [CO], [Cl2], and [COCl2] represent the molar concentrations of CO, Cl2, and COCl2, respectively, at equilibrium.