A limiting reactant is the substance that is fully consumed during a chemical reaction. Once the limiting reactant has been fully consumed, the chemical reaction stops. In some instances, the limiting reactant is known as a limiting reagent.
A limiting reactant determines the amount of product that is formed after a chemical reaction process takes place. If another substance remains after the reaction, it is normally called an excess reactant. This is because it has nothing to react with in order to produce an end product.
To find the difference between these two, calculations must be made to determine which of the two substances produces more on its own. A limiting reactant will normally produce the lesser amount of the end product when compared to an excess reactant.
If, for example, four tires and four headlights are needed to complete a car design but there are two headlights and five tires, the limiting reactant in this scenario would be the headlights. This is because without two extra headlights, the car will not be a complete product. In the same scenario, the tires are considered the excess reactant since there will still be an extra tire after using the other four tires available.