Choose a chemical reaction involving two or more reactants. For this reaction, how do you determine which reactant or reactants are limiting? Explain.

Answer 1

S + O2 ==> SO2
Suppose you have 16 g S and 32 g O2 and they react.
mols S = grams/atomic mass = 16/32 = 0.5 mol S.
mols O = 32/32 = 1 mol O2.

0.5 mol S requires, from the coefficients in the balanced equation, 0.5 mol O2. Do you have that much O2. Yes, so S is the limiting reagent.
Suppose you didn't start with S for the logic but started with O2. You have 1 mols O2, it will take 1 mol S to react with it (again look at the coefficients). Do you have 1 mol S. No, so S must be the limiting reagent.