Question

At 1000 K, a sample of pure NO2 gas decomposes: 2NO2(g) ⇌ 2NO(g) + O2(g) The equilibrium constant, KP, is 158. Analysis shows that the partial pressure of O2 is 0.45 atm at equilibrium. Calculate the pressure of NO and NO2 in the mixture

Answer 1

2 NO2 (g)       <—>   2NO (g)   +   O2 (g)

p               0           0       (initial)

p-2x               2x           x       (at equilibrium)

Given:

pO2 = 0.45 atm

x = 0.45 atm

pNO = 2x = 2*0.45 = 0.90 atm

Now use:

Kp = p(NO)^2 p(O2) / p(NO2)^2

158 = 0.90^2 * 0.45 / p(NO2)^2

p(NO2)^2 = 2.307*10^-3

pNO2 = 0.0480 atm

pressure of NO = 0.90 atm

pressure of NO2 = 0.0480 atm