2 NO2(g) ⇄ N2O4(g) dark brown colorless The dimerization of NO2(g) , an exothermic process, is represented by the equation above. A 0.0688 mol sample of NO2(g) is placed in a rigid 1.00 L reaction vessel and allowed to reach equilibrium at a certain temperature. What is the value of Kc at this temperature if 0.0133 mol of N2O4(g) is present at equilibrium?