What happens to a ratio when an excess quantity of a reactant exists?

Question

Naomi Aronson · Accepted Answer

Nothing. A significant excess of one reactant over another in a two component reaction simply guarantees that the reactant in lower amount is completely consumed.

Regardless of the quantities of reagents mixed in a reaction, the reaction ratio will remain the same. One reactant will be totally consumed and any other reactants will remain in excess unreacted. Example: Assume 5 moles of each reactant in the following equation is mixed and the process goes to completion. #2NO(g) + O_2(g) => 2NO_2(g)# All of the #NO(g)# will be consumed but only 2.5 moles of #O_2(g)# will be consumed leaving 2.5 moles of the oxygen in excess. The mole amount of #NO(g)# consumed in the reaction will always be twice the mole amount of #O_2(g)# consumed regardless of the mole amounts of each reagent mixed.

Cameron Andrews · Answer

undefined When an excess quantity of a reactant exists, the ratio of the reactants in the reaction mixture changes. This is because the limiting reactant, which determines the amount of product formed, is no longer limiting. As a result, the ratio of reactants originally required for the reaction is not maintained, and the excess reactant is left over after the reaction is complete.