Kc for the reaction N2(g) + O2(g) ⇀↽ 2 NO(g) at 1200◦C is 1 × 10−5 What is the equilibrium molar concentration of NO?

Question

The equilibrium constant Kc for the reaction

N2(g) + O2(g) ⇀↽ 2 NO(g)

at 1200◦C is 1 × 10−5

. What is the equilibrium molar concentration of NO in a 12 L

reaction vessel that initially held 0.076 mol

N2 and 0.427 mol O2?

Answer in units of mol/L

Answer 1

Kc = [NO]^2 / [N2][O2] = 1X10^-5

Set up an ICE table:

...................[N2]...............[O2]...........[NO]

initial......6.33X10^-3....0.0356...........0

Change.......-x...................-x..............+2x

Equil.....6.33X10^-3-x....0.0356-x......2x

Because K is very small, initially assume that x will be insignificant compared to 6.33X10^-3 and to 0.0356. Then,

Kc = 1X10^-5 = x^2 / (6.33X10^-3)(0.0356)

x = 4.7X10^-5 M

[NO] = 2x = 9.5X10^-5 M