Law of conservation of mass — Science definition
Defined in 2 courses:
- In a chemical reaction, the total mass of the reactants equals the total mass of the products. (Physical Science: Matter, Forces & Energy)
- In any chemical reaction, atoms are only rearranged, so the total mass of reactants equals the total mass of products. (Physical Science: Chemistry)
Where it is taught
- Conservation of Mass — Chemistry, Physical Science: Matter, Forces & Energy, Grade 8
- Balancing Chemical Equations — Reactions, Moles & Composition, Physical Science: Chemistry, Grade 11
In use
The law of conservation of mass accounts for all relevant matter.
Conservation of Mass
But an equation is only trustworthy if it obeys the law of conservation of mass.
Balancing Chemical Equations
Questions using law of conservation of mass
Problem 1
The law of conservation of mass says that in a chemical reaction…
- mass can be created but not destroyed
- the total mass of the reactants equals the total mass of the products
- products always weigh less than the reactants
- atoms are destroyed and new ones form
Answer and explanation
the total mass of the reactants equals the total mass of the products
Conservation of mass means reactant mass and product mass are always equal in a closed system.
Problem 2
Explain how balancing a chemical equation is a direct application of the law of conservation of mass.
Answer and explanation
Conservation of mass says atoms are only rearranged, never created or destroyed, so the same number of each atom must appear on both sides. Balancing forces the atom counts to match, which guarantees the total mass of the reactants equals the total mass of the products.
Taught alongside
- closed system
- model
- evidence
- system boundary
- assumption
- chemical equation
- coefficient
- subscript
- balanced equation