Question

An equilibrium mixture of dinitrogen tetroxide and nitrogen dioxide is 68.5% nitrogen dioxide by mass at 1 atm and 25 degrees celsius. What is the keq for this reaction?

Answer 1

Solution.

The equilibrium reaction is

Let's assume we have 1000 g of total mass. In this case m(NO₂) = 685 g and m(N₂O₄) = 1000-685 = 315 g;

The corresponding amounts of substances are

n(NO₂) = 685/46.0 = 14.9 moles;

n(N₂O₄) = 315/92 = 3.42 moles;

The total number of moles os 14.9+3.42 = 18.32; assuming the ideal gas behaviour, the mole fractions are proportional to a partial pressures, so that

P(NO₂) =(14.9/18.32)*101325 = 82410 Pa;

P(N₂O₄) = 101325- 82410 = 18910 Pa;

The pressure equilibrium constant is