Question

Phosgene (COCl2) is a very toxic molecule that was used as a chemical weapon in World War I. It can also be a precursor to chemicals used to make closed-cell polyurethane insulation, which has a very high R value. Phosgene can decompose according to the following equilibrium reaction. The KP for this reaction is 6.8 x 10-9 at 373 Kelvin. Calculate the equilibrium pressures of each gas if a container initially contains phosgene with a partial pressure of 2 atm. COCl2(g) equilibrium reaction arrow CO(g) + Cl2(g)

Answer 1

COCl2(g) CO(g) + Cl2(g)

KP for this reaction is 6.8 x 10-9 at 373 kelvin.

initial partial pressure of phosgene = 2 atm

                 COCl2(g)                CO(g)        +      Cl2(g)

initial partial pressure           2 atm                                  0                       0

at equilibrium                       (2-X)                                   X                       X

we know that,

KP = [PCO] [PCl2] / [PCOCl2]

KP = [X] [X] / [2-X]

6.8 X 10-9 = [X]2 / [2-X]

we get this equation

X² + 6.8*10^-9 - 13.6*10^-9 = 0

after solving this quadratic equation we get two x values, 0.0001166 and -0.0001166, we are get positive no. so we choose X = 0.0001166

put the value of X in above formula we get,

Pco = 0.0001166

Pcl2 = 0.0001166

Pcocl2 = 2- 0.0001166 = 1.99