Question

Dinitrogen tetroxide decomposes to nitrogen dioxide. Write the balanced chemical equation for this reaction. Start with pure N₂O₄ at 1.00 atm. Find the equilibrium partial pressures of N₂O₄ and NO₂. The equilibrium constant for this reaction is K = 11.

Answer 1

                                                                        N₂O₄ (g) 2 NO₂ (g)

Initial pressure                                         1.00                0

Change in pressure                                          - X                 2X

Equilibrium pressure                                    (1.00 - X)            2X

or, 11 = (2X)²/(1.00 - X)

or, 11 = 4X²/(1.00 - X)

or, 4X² + 11X - 11 = 0

or,

or,

or,

or, X = 0.775 atm, - 3.53 atm

The acceptable value of X = 0.775 atm as partial pressure can not be negative.

Therefore, the equilibrium partial pressure of N₂O₄ = (1.00 - 0.775) = 0.225 atm

And the equilibrium partial pressure of NO₂ = 2 x 0.775 = 1.55 atm