What is the term for the reactant that is completely consumed in a chemical reaction?

The term for the reactant that is completely consumed in a chemical reaction is known as the limiting reactant. This reactant determines the maximum amount of product that can be formed because once it is used up, the reaction stops, regardless of the amounts of other reactants present.

In a chemical reaction, if one reactant is in insufficient quantity compared to the others, it limits the extent of the reaction, hence the name "limiting reactant." Understanding this concept is essential for stoichiometric calculations in chemistry, as it allows chemists to predict how much product can be formed from given quantities of reactants.

For clarity, the other terms listed do not apply. The excess reactant refers to any reactants that are present in greater amounts than necessary and remain unreacted once the limiting reactant has been fully consumed. Intermediate reactants are species that are formed during the reaction process but are not included in the initial reactants. Byproducts are products formed in addition to the primary product of a reaction, often as unintended outputs of the reaction process.