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How does the law of conservation of mass apply to chemical reactions?

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combustion — chemical reaction Log burning in a fire. Burning wood is an example of a chemical reaction in which wood in the presence of heat and oxygen is transformed into carbon dioxide, water vapor, and ash.

The law of conservation of mass states that matter cannot be created or destroyed during a chemical reaction. Because atoms are simply rearranged into new substances rather than being created or destroyed, the total mass of the reactants must equal the total mass of the products.1234

This principle is the fundamental basis for balancing chemical equations. To satisfy the law, an equation must have the same number of atoms of each element on both sides. Chemists achieve this by adjusting coefficients—the numbers placed in front of chemical formulas—to ensure that the mass of the substances entering the reaction matches the mass of the substances produced.32

Historically, this concept was championed by Antoine Lavoisier, who insisted that chemists weigh all substances involved in their experiments to demonstrate that mass remains constant. Today, this principle remains a cornerstone of modern chemistry, allowing scientists to use stoichiometry to calculate precise mass relationships between reactants and products.13