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 0.255 at 1200 °C. If a container is charged with 0.487 atm of nitrogen and 0.183 atm of oxygen and the mixture is allowed to reach equilibrium, what will be the equilibrium partial pressure of nitrogen? Report your answer to three significant figures.

Answer 1

                 N₂(g)     +      O₂(g)      ⇌        2NO(g)

initial       0.487            0.183                    0

at equi    (0.487 - x)    ( 0.183 - x)           2x

Kp = (p NO)^2 / (p N2 * p O2)

0.255 = (2x)^2 / ((0.487 - x)(0.183 - x))

x = 0.05836

p NO = 2 * 0.05836 = 0.117

p N2 = (0.487 - 0.05836) = 0.429

p O2 = (0.183 -0.05836) = 0.125