Chemical Kinetics

Chemical Kinetics

Question

The reaction N2(g) + O2(g)   2NO(g), contributes to air pollution whenever a fuel is burnt in air at a high temperature. At 1500 K, equilibrium constant K for it is 1.0 x 10-5. Suppose in a case [N2] = 0.80 mol L-1and [O2] = 0.20 mol L-1 before any reaction occurs. Calculate the equilibrium concentrations of the reactants and the product after the mixture has been heated to 1500 K.

Answer

N2(g) + O2(g) rightwards harpoon over leftwards harpoon2NO(g)

 

T=0         0.8     0.20

T=t          0.8-x   0.2-x  2x

Kc = 1.0 x 10-5

Kc = fraction numerator left square bracket bold italic N bold italic O right square bracket squared over denominator left square bracket bold italic N subscript 2 right square bracket space left square bracket bold italic O right square bracket end fraction

Or, 1.0 x 10-5 = (2x)2/ [(0.8 – x)(0.2 – x )]

If x is very small, then

0.8 – x  0.8

0.2 – x  0.2

1.0 x 10-5 = (2x)2 / [(0.80) (0.2)]

16 x (10-6) = 4 x2

X2 = 2 x 10-3

Therefore, the amount of reactant and product at equilibrium is as follows:

N2 = 0.8 - 0.002 = 0.798

O2 = 0.2 - 0.002 = 0.198

NO = 2x = 2 x 2 x 10-3 = 4 x 10-3

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