## Chemistry and Chemical Reactivity (9th Edition)

Notice that graphite, as a solid, isn't factored in the equilibrium. For CO2, the reacted concentration being x, leads to, by stoichiometry, a final concentration of CO of 2x. $K=[CO]^2/[CO_2]$ $0.021=(2x)^2/(0.012-x)$ $0.000252-0.021x=4x^2\rightarrow 4x^2+0.021x-0.000252=0$ $x=+0.0057\ or\ -0.011\rightarrow x=0.0057\ M$ The equilibrium concentration of CO is 2x: $0.0114\ M$