Step-by-step explanation:
2NH3(g) --> 3H2(g) + N2(g)
The equlibrium constant is the ratio of the concentration of products to that of reactants.
Keq = [Products] / [Reactants]
So to write the expression, we have to identify our reactants and products.
Reactants = NH3
Products = H2 and N2
The coefficients are expressed as powers of the entities in the expression, this leads us to;
[Products] = [H2]² [ N2]
[Reactants] = [NH3]³
Keq = [NH3]³ / [H2]² [ N2]