Excess reactant

Definition

An excess reactant is a substance that remains after a chemical reaction has reached completion. It is the reactant that is not entirely consumed in the reaction.

5 Must Know Facts For Your Next Test

1. The excess reactant is left over because it is present in a greater quantity than necessary to completely react with the limiting reactant.
2. Identifying the excess reactant requires calculating the amount of product formed by each reactant and comparing them.
3. The limiting reactant determines when the reaction stops, while the excess reactant does not affect this point.
4. Excess reactants can be recovered and reused in industrial processes to improve efficiency and reduce waste.
5. Stoichiometric calculations involving excess and limiting reactants are essential for accurately predicting reaction yields.

Review Questions

• How do you determine which reactant is the excess reactant in a chemical reaction?
• Why might an industrial chemist be interested in identifying and recovering an excess reactant?
• What role does the excess reactant play in determining the theoretical yield of a reaction?

Related terms

Limiting Reactant:

The substance that is completely consumed first in a chemical reaction, thereby determining when the reaction stops.

Theoretical Yield:

The maximum amount of product that could be formed from given amounts of reactants, assuming complete conversion.

Stoichiometry:

The calculation of quantities of substances involved in chemical reactions based on balanced chemical equations.