Excess Reagent
A reactant present in a greater amount than is needed to consume the limiting reagent completely.
Formula / equation
n_excess = n_initial − n_reacted
Unit
mol
In depth
Some of an excess reagent remains unreacted at the end and must be separated from the product. Chemists deliberately use an excess of a cheap or easily removed reactant to drive an expensive one to complete conversion, a strategy justified by Le Chatelier's principle in reversible systems.
Examples in the real world
Burning a hydrocarbon in excess air ensures complete combustion; leftover oxygen is simply vented.