A gas mixture containing nitrogen and hydrogen, maintained at a temperature of $500\,$K, was introduced into an evacuated vessel with a volume of $6.0\,\text{dm}^3$. The vessel was then sealed. $\text{N}_2(g) + 3\text{H}_2(g) \rightleftharpoons 2\text{NH}_3(g)$ The mixture was left until equilibrium was reached. It was found that $7.2\,$mol of $\text{N}_2$ and $12.0\,$mol of $\text{H}_2$ were present in the equilibrium mixture. For this equilibrium, the equilibrium constant, $K_c$, has a value of $6.0 \times 10^{-2}$ at $500\,$K. What is the concentration of ammonia in the equilibrium mixture at $500\,$K?
- A$0.58\,\text{mol dm}^{-3}$
- B$0.76\,\text{mol dm}^{-3}$
- C$3.5\,\text{mol dm}^{-3}$
- D$27\,\text{mol dm}^{-3}$