If you want to check:
The reversible reaction N2(g) + 3H2(g) ? 2NH3(g) produces ammonia, which is a fertilizer. At equilibrium, a 1-L flask contains 0.15 mol H2, 0.25 mol N2, and 0.10 mol NH3. Calculate Keq for the reaction.
keq = [C]^c X [D]^d/[A]^a X ^b
In this scenario, [A] is the concentration of N2, [B] is the concentration of H2 and [C] is the concentration of NH3. There is no [D], as no fourth reagent is included. For this equilibrium quotient thing, you always take what is behind the double arrow as the top number, demonstrated earlier in this sentence.
a, b, c stand for the amount of mole there is relative to each other. In this reaction, a is 1, b is 3 and c is 2.
That gives us:
Keq = [NH3]^2 / [N2]^1 * [H2]^3
Now, you have a 1 litre flask. That means that the mol given is instantly also the concentration. Respectively:
0.15 mol/litre H2, 0.25 mol/litre N2, 0.10 mol/litre NH3.
In the formula, this gives us:
Keq = 0.10^2 / (0.25 * 0.15^3)
Keq = 0.01 / (0.25 * 0.003375)
Keq = 0.01 / (0.00084375)
Keq = 11.8518519
..I think, anyway. I might have made a mistake somewhere. This should give you a general idea of how to do this though.
Note that you can never use liquids or solids in this formula, only gases and solutions.
Been SUCH a long time since i've done chemistry and had to remove myself from the class during rate reactions. However looking at your methodology Oranos it looks correct the only thing I would scrutinize would be the written out method:
[b]Keq = 0.10^2 / (0.25 * 0.15^3)
Keq = 0.01 / (0.25 * 0.003375)
Keq = 0.01 / (0.00084375)
Keq = 11.8518519
Otherwise everything looks correct imho from what I remember in chemistry class. Was about to stop and say that the number for nitrogen didn't look right, but it was.