Question

The air pollutant NO is produced in automobile engines from the high-temperature reaction N2(g)+O2(g)←−→2NO(g);Kc=1.7×10−3 at 2300 K. The initial concentrations of N2 and O2 at 2300 K are both 1.80 M. Part A:What is the concentration of NO when the reaction mixture reaches equilibrium? Part B:What is the concentration of N2 when the reaction mixture reaches equilibrium? Part C:What is the concentration of O2 when the reaction mixture reaches equilibrium?

Answer 1

First, let us define the equilibrium constant for any species:

The equilibrium constant will relate product and reactants distribution. It is similar to a ratio

The equilibrium is given by

rReactants -> pProducts

Keq = [products]^p / [reactants]^r

For a specific case:

aA + bB = cC + dD

Keq = [C]^c * [D]^d / ([A]^a * [B]^b)

Kc = [NO]^2 /([N2][O2])

initially

[N2] = [O2] = 1.8

[NO] = 0

in equilbirium

[N2] = [O2] = 1.8 - x

[NO] = 0 + 2x

substitute

Kc = [NO]^2 /([N2][O2])

1.7*10^-3 = (2x)^2 /(1.8 - x)^2

sqrt(1.7*10^-3) = 2x/(1.8-x)

0.0412*1.8 - 0.0412x = 2x

(2+0.0412) X =0.0412*1.8

x = 0.0412*1.8 /(2+0.0412)

x = 0.0363

[N2] = [O2] = 1.8 - 0.0363 = 1.7637 M

[NO] = 0 + 2*0.0363 = 0.0726 M