Chemists studied the formation of phosgene by sealing 0.81 atm of carbon monoxide and 1.37 atm of chlorine in a reactor at a certain temperature. The pressure dropped smoothly to 1.55 atm as the system reached equilbrium. Calculate Kp (in atm-1) for
CO(g) + Cl2(g) ↔ COCl2(g)