# What is the equilibrium constant expression for the equation C(s) + O_2(g) rightleftharpoons CO_2(g)?

${K}_{e q}$ $=$ $\frac{\left[C {O}_{2} \left(g\right)\right]}{\left[{O}_{2} \left(g\right)\right]}$
Carbon does not appear in the equilibrium expression, because, as a solid, it does not have a concentration. As written above, ${K}_{e q}$ would probably be unmeasurably large.