what is Kc for the reaction?

Question

When 0.60 mol NH₃ is decomposed in a 1 Liter flask at 850 K, the equilibrium concentration of NH₃ is measured as 0.12 M. Given that ammonia decomposes according to the reaction 2 NH₃(g) <=> N₂ (g) + 3H₂ (g), what is Kc for the reaction?

The correct answer is 6.22

Answer 1

2NH₃(g) <===> N₂(g) + 3H₂(g)

0.60......................0............0........Initial

-2x.......................+x........+3x.......Change

0.12.....................0.24.....0.72.....Equilibrium

Kc = [N₂][H₂]³ / [NH₃]²

Kc = (0.24)(0.72)³ / (0.12)²

Kc = 6.22