What does the term "limiting reagent" refer to in a chemical reaction?

The term "limiting reagent" refers to the reactant that is completely consumed first in a chemical reaction. This concept is crucial because it determines the maximum amount of product that can be formed. In a chemical reaction, reactants are combined in specific ratios based on their stoichiometric coefficients. When one of these reactants is entirely used up before the others, it limits the extent of the reaction and thus limits the amount of product produced.

For example, if you are mixing hydrogen gas and oxygen gas to produce water, the amounts of these gases must be in a specific ratio, as indicated by the balanced equation. If you have plenty of oxygen but not enough hydrogen, the hydrogen will be the limiting reagent, and the reaction will stop when all the hydrogen is consumed, regardless of the excess oxygen present.

Understanding the limiting reagent is integral when calculating yields and understanding the efficiency of reactions, as it directly influences how much product can ultimately be formed.