Final answer:
The limiting reactant in a chemical reaction determines the maximum quantity of product that can be formed and causes the reaction to cease once it is depleted.
Step-by-step explanation:
In a chemical reaction, the limiting reactant is the substance that is completely consumed first, and as a result, determines the maximum amount of product that can be formed from the reactants. The other reactants that are not entirely used up are considered to be in excess.
Therefore, the limiting reactant performs two critical roles: it dictates the quantity of product formed and it restricts the reaction because no further product can form once the limiting reactant is depleted. A useful strategy in chemical analysis is to compare the amount of product that each reactant could theoretically produce based on the reaction's stoichiometry; the reactant that yields the lesser amount of product is the limiting one. Identifying the limiting reactant is essential for efficiently calculating the expected yield of a chemical reaction.