Stoichiometry Module: Limiting Reactants
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Limiting Reactants

S'Mores Example If you have not read the s'mores example, click on the s'more on the left.

The s'mores example is an example of an ingredient being limited. Enough graham crackers were purchased to make 35 s'mores, but only 32 could be made. The s'more production was limited by the amount of chocolate you had available.

This situation often occurs in chemical reactions. Reactants are mixed together and products will be formed until one of the reactants is gone. The reactant that is the first to run out is said to be limiting.

Aspirin is made by reacting salicylic acid and acetic anhydride. The balanced chemical reaction for this process is:


Move mouse over formulas to show names.

If 20 moles salicylic acid are added to 20 moles acetic anhydride, which reactant will run out first?

Salicylic acid Acetic anhydride They will run out at the same time

Good! Since every mole of acetic anhydride will react with two moles of salicylic acid, the 20 moles of salicylic acid be gone after only 10 moles of acetic anhydride have reacted.

Remember every mole of acetic anhydride reacts with two moles of salicylic acid. Try again