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Reactants

Written by the Fiveable Content Team • Last updated August 2025
Written by the Fiveable Content Team • Last updated August 2025

Definition

Reactants are the starting substances that undergo chemical changes in a reaction. They are present before the reaction begins and are transformed into products.

AP course connection

Topic 2.1: 2.1 Atoms, Isotopes, Ions, and Molecules: The Building Blocks

Unit 2

Keep studying

Review this concept in 2.1 Atoms, Isotopes, Ions, and Molecules: The Building BlocksGeneral Biology I course hub

reactants cheat sheet for homework

visual study aid

5 Must Know Facts For Your Next Test

  1. Reactants are consumed during a chemical reaction.
  2. The amount of reactants determines the quantity of products formed.
  3. Reactants can be elements, compounds, or molecules.
  4. In a balanced chemical equation, reactants are listed on the left side.
  5. The rate at which reactants are used up can affect the speed of the reaction.

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