A 3.50 L flаsk initiаlly cоntаins 0.455 mоles оf Cl2 and 0.658 moles of H2O. When the contents of the flask reach equilibrium, O2 is present in a concentration of 0.0279 M. What is the molar concentration of H2O (g) at equilibrium? 2 Cl2(g) + 2 H2O(g) ⇌ 4 HCl(g) + O2(g)