Why are reactants added in excess during a chemical reaction?

Adding reactants in excess during a chemical reaction helps ensure that the limiting reactant is completely consumed. The limiting reactant is the substance that is entirely used up first, thus determining the maximum amount of product that can be formed. By providing an excess of other reactants, you can guarantee that there is enough of them available to react fully with the limiting reactant, maximizing the yield of the desired product. This is especially important in industrial and laboratory processes where efficiency and yield are crucial.

Offering an abundance of reactants avoids situations where some of the limiting reactant remains unreacted, potentially reducing the efficiency of the reaction and the amount of product produced.