Question

Nitric oxide is formed in automobile exhaust when nitrogen and oxygen in air react at high temperatures.

N₂(g) + O₂(g) ⇌ 2NO(g)

The equilibrium constant K_p for the reaction is 0.14 at 1200 °C. If a container is charged with 0.175 atm of nitrogen and 0.127 atm of oxygen and the mixture is allowed to reach equilibrium, what will be the equilibrium partial pressure of oxygen? Report your answer to three significant figures.

Answer 1

Reaction: N2 (g) + O2 (g) ----> 2NO (g)

Initially:    0.175      0.127            0

Change:   -p            -p                +2p

Final:     0.175-p    0.127-p         2p

Kp = (2p)^2 / (0.175-p) * (0.127-p)

=> 0.14 = 4p^2 / (0.175-p) * (0.127-p)

=> 3.86 p^2 + 0.04228 p - 0.0031115 = 0

Solving the above quadratic equation, we get

p = 0.0234 atm

Equilibrium Partial Pressure of O2 =0.127 - p = 0.127 - 0.0234 = 0.104 atm