A limiting reactant (or limiting reagent) is the substance in a chemical reaction that is completely used up first. Because it runs out before the other reactants, it determines how much product can be formed.
Key points:
- Once the limiting reactant is finished, the reaction stops, even if other reactants are still available.
- The limiting reactant controls the maximum amount of product that can be made.
- The other reactant(s) that remain after the reaction are called excess reactants.
- Identifying the limiting reactant is important in chemistry, industry, and even daily life to avoid waste and to know the exact yield of a reaction.
Simple example: If you are making sandwiches and you have 8 slices of bread and only 3 slices of cheese, the cheese is the limiting reactant because it runs out first. The number of sandwiches you can make is limited by the amount of cheese, not the bread.