The equation for the following reaction and the value of Kc at a given temperature are given.

An equilibrium mixture in a 5.00 L flask contains 0.25 mol of PCl5 and 0.16 mol of PCl3. What equilibrium concentration of Cl2 must be present?
PCl3 (g) + Cl2 (g) --------> PCl5 (g) Kc = 1.9

[PCl5] = 0.25mol/5L = 0.05M
[PCl3] = 0.16mol/5L = 0.032M
Kc = 1.9 = [PCl5] / ([PCl3] x [Cl2]) = 1.9
[Cl2] = [PCl5] / ([PCl3] x1.9 = 0.05 / (0.032 x 1.9) = 0.82M