Consider the following equilibrium process at $\pu{686 ^\circ C}$: $$\ce{CO2(g) + H2(g) <=> CO(g) + H2O(g)}$$
The equilibrium concentrations of the reacting species are $[\ce{CO}] = \pu{0.050 M}$, $[\ce{H2}] = \pu{0.045 M}$, $[\ce{CO2}] = \pu{0.086 M}$, and $[\ce{H2O}] = \pu{0.040 M}$. (a) Calculate $K_c$ for the reaction at $\pu{686 ^\circ C}$. (b) If we add $\ce{CO2}$ to increase its concentration to $\ce{0.50 mol/L}$, what will the concentrations of all the gases be when equilibrium is reestablished?
I've answered (a) already, and I got $K_p$ and $K_c$ both equal to $0.52$; in other words, I'm certain that the system is in equilibrium. However, I'm having trouble answering (b). Do just add $\pu{0.50 mol/L}$ to all the other concentrations?