Question

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

Answer 1

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.

Explanation:

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.