36g of H₂O will be formed.
The limiting reagent is the reactant that is completely used up in a reaction, and thus determines when the reaction stops. From the reaction stoichiometry, the exact amount of reactant needed to react with another element can be calculated.
If the reactants are not mixed in the correct stoichiometric proportions (as indicated by the balanced chemical equation), then one of the reactants will be entirely consumed while another will be left over. The limiting reagent is the one that is totally consumed; it limits the reaction from continuing because there is none left to react with the in-excess reactant.
There are two ways to determine the limiting reagent:
One method is to find and compare the mole ratio of the reactants used in the reaction.
Another way is to calculate the grams of products produced from the given quantities of reactants; the reactant that produces the smallest amount of product is the limiting reagent.
Learn how to calculate limiting reactant of a chemical reaction at Chemistry.about.com.
Determine the limiting reagent of your chemical reactions and equations using this online tool shared by en.intl.chemicalaid.com.