Answer to Question #21243 in Physical Chemistry for nidhi mehra

Question

the reaction N2+O2=2NO2 contributes to air pollution. whenever a fuel is burnt in air at high temp. At 1500 K equilibrium constant K for it is 1.0*10^-5. suppose in a case [N2]=0.80 mol per litre and [O2]= 0.20 mol per litre before any reaction occurs. Calculate the equillibrium concerntrations of the reactants and the products after the mixture has been heated to 1500 K.

Answer 1

Equilibrium constant can be calculated by next equation:

K = [products]/[reactants]

K = [NO₂]²/[O₂][N₂]

Concentration after reaction would be: (where x is that part
of reactants that would be converted in product)

0.8-x 0.2-x 2x
N₂ + O₂ = 2NO₂
In the moment at equilibrium equilibrium constant would be:

K = [2x]²/[0.8-x][0.2-x]

1.0*10^-5 * (0.8-x)*( 0.2-x) = 4x²

1.0*10^-5 * (0.6-0.8x-0.2x+x^2) = 4x²

6.0*10^-6 - 6.0*10^-6 x + 1.0*10^-5x^2 - 4x^2 = 0

x = 0.001224 M so concentration of product NO₂ m = 2*0.001224 = 0.002448 M

concentration of O₂ = 0.2-0.001224 = 0.198776 and concentration of N₂ = 0.798776 M