Final answer:
The limiting reactant is the reactant that determines the amount of product in a chemical reaction. It is completely used up. The excess reactant is the reactant initially present in a greater amount that is left over after the reaction is complete.
Step-by-step explanation:
The limiting reactant is the reactant that determines the amount of product that can be formed in a chemical reaction. It is the reactant that is completely used up. To identify the limiting reactant, you can use stoichiometry to find the mass of product produced by each individual reactant. The reactant that produces a lesser amount of product is the limiting reactant.
The reactant that is initially present in a greater amount than will eventually be reacted is called the excess reactant. There is always excess reactant left over after the reaction is complete. In a balanced chemical equation, the stoichiometric ratio of the reactants can be used to compare the amounts of each reactant provided.
To determine the limiting reactant and excess reactant, compute the molar amounts of each reactant provided and compare them to the stoichiometric amounts in the balanced chemical equation. Whichever reactant gives the lesser amount of product is the limiting reactant, and the other reactant is the excess reactant.