Carbon tetrachloride reacts at high temperatures with oxygen to produce two toxic gases, phosgene and chlorine.

CCl4(g) + 1/2O2(g) COCl2(g) + Cl2(g), Kc = 4.4 × 109 at 1,000 K
Calculate Kc for the reaction 2CCl4(g) + O2(g) 2COCl2(g) + 2Cl2(g).