Answer – An excess reactant is one that remains after a chemical reaction is complete.
Explanation:
Balanced chemical equations indicate the ideal proportions of reactants required to form a product. In the real world, however, inexact quantities of reactants are used. This leads to one of the reactants being consumed completely with the rest being left behind in varying amounts at the end.
Those reactants that remain after a reaction is complete/reaches equilibrium are known as excess reactants. As the name suggests, they are present in excess of what is necessary for the reaction to be completed.
For example:
Two moles of solid sodium need to react with one mole of chlorine gas to form two moles of sodium chloride. This means that Na and Cl combine in a 2:1 ratio.
Consider having 2 moles of sodium and 2 moles of chlorine gas to perform this reaction. As per the above equation, all of the sodium gets used up but only 1 mole of chlorine gas is utilized. The remaining 1 mole of chlorine gas in such a case is the excess reactant.
