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💏intro to chemistry review

Conservation of Mass

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

Definition

Conservation of mass is a fundamental principle in chemistry which states that the total mass of a closed system remains constant, regardless of any physical or chemical changes that may occur within the system. This means that the mass of the reactants in a chemical reaction must be equal to the mass of the products.

5 Must Know Facts For Your Next Test

  1. Conservation of mass is a fundamental law of nature and is one of the most important principles in chemistry.
  2. Conservation of mass applies to both physical and chemical changes, as long as no matter enters or leaves the system.
  3. The total mass of the reactants in a chemical reaction must be equal to the total mass of the products.
  4. Mass can be converted into energy, but the total mass-energy of a closed system remains constant.
  5. Conservation of mass is the basis for many important chemical calculations, such as stoichiometry and the balancing of chemical equations.

Review Questions

  • Explain how the principle of conservation of mass is applied in the context of a chemical reaction.
    • In a chemical reaction, the principle of conservation of mass states that the total mass of the reactants must be equal to the total mass of the products. This means that the atoms present in the reactants are rearranged during the reaction, but the total number of atoms and their individual masses remain the same. This principle is the foundation for balancing chemical equations and performing stoichiometric calculations, as the mass of the reactants and products must be conserved.
  • Describe how the concept of a closed system relates to the conservation of mass.
    • A closed system is a system that does not exchange matter with its surroundings, but may exchange energy. In the context of conservation of mass, a closed system is essential because it ensures that no matter enters or leaves the system during a physical or chemical process. This allows the total mass of the system to remain constant, as required by the principle of conservation of mass. If a system were to exchange matter with its surroundings, the total mass would not be conserved, and the principle would not apply.
  • Analyze how the conservation of mass principle is used to ensure the accuracy of chemical measurements and calculations.
    • The conservation of mass principle is crucial for ensuring the accuracy of chemical measurements and calculations, such as those involved in stoichiometry and the balancing of chemical equations. By requiring that the total mass of the reactants be equal to the total mass of the products, the conservation of mass principle provides a way to verify the completeness and accuracy of chemical processes. If the masses do not balance, it indicates an error in the measurements or the underlying chemical reaction. This principle allows chemists to confidently rely on the results of their experiments and calculations, as they can be sure that mass is being conserved throughout the process.