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

1 Answer
May 22, 2017


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.


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.