# What is the difference between a limiting reactant and an excess reactant?

The image below represents the reaction between hydrogen and oxygen gas to produce water. 4 molecules of $\text{H"_2}$ react with 3 molecules of $\text{O"_2}$. The products include 4 molecules of water and 1 molecule of oxygen gas that didn't react. In this case the limiting reactant is $\text{H"_2}$ and the excess reactant is $\text{O"_2}$.