This is a general approach to reaction stoichiometry. It will help you calculate limiting reagents, theoretical yields, enthalpy changes of reaction, and it will give you insight into reaction rates.
Consider the following problem:
You have 10.0 grams each of nitrogen and hydrogen. How much ammonia can you produce? The reaction is
N2 + 3 H2 → 2 NH3
The first step (no matter which approach you use) is to convert to moles:
The next step is to compute the number of "mole reactions" of each substance. The number of mol-rxns is calculated by dividing the number of moles you have by the coefficient of the substance in the balanced reaction (in this reaction, the coefficient of N2 is 1 and the coefficient of H2 is 3 as shown in row 3 below). For example, we start with 4.96 moles of hydrogen, but since the stoichiometric coefficient of H2 in the reaction is 3, we only have 1.65 mol-rxns of H2.
Now, whichever reactant has the least number of mol-rxns, that is the limiting reagent. So here, nitrogen is the limiting reagent, with 0.357 mol-rxns.
This also tells you that the reaction will run, as written, 0.357 times. You will use up 0.357 mol-rxns of EVERY reagent, and you will produce 0.357 mol-rxns of product (row 5 in the following table). You can now compute the mol-rxns of everything after the reaction completes (row 6), and convert back to moles in row 7 (by multiplying by the reaction coefficients, row 3) and finally to grams (row 8).
This might seem like extra steps, and in some cases it is. However, it is ONE approach that works for ALL stoichiometry questions. It will also be useful in our later studies of thermochemistry, and it will simplify things when you get to reaction kinetics in CHY 115.