Chemistry Regents Practice Test 2025 - Free Chemistry Regents Practice Questions and Study Guide

The limiting reactant is defined as the reactant that is completely consumed during a chemical reaction, which limits the amount of product that can be formed. In a chemical reaction, reactants combine in specific ratios based on their stoichiometry, and one of the reactants will often run out before the others. This reactant effectively determines how much product can be produced because once it is used up, the reaction cannot continue, even if other reactants are still available.

Understanding this concept is essential for calculating yield and understanding reaction efficiency. It helps chemists optimize reactant amounts to maximize product formation while minimizing waste. In contrast, a reactant that is left over after a reaction, one that determines the rate of the reaction, or one that is present in excess does not influence the overall extent of the reaction in the same way as the limiting reactant does.