An initial mixture of nitrogen gas and hydrogen gas are allowed to react in order to reach equilibrium by the following reaction:
3 H2(g) + N2(g) ? 2 NH3(g)
At equilibrium, [H2] = 5.0 M, [N2] = 8.0 M and [NH3] = 4.0 M. What was the initial concentration of H2(g) before any reaction occurred?