Conservation of Mass and Balancing Equations

This lesson covers the law of conservation of mass and how to balance chemical equations. These concepts are fundamental to all quantitative chemistry and are required by the Edexcel GCSE Chemistry specification (1CH0).

---

The Law of Conservation of Mass

The law of conservation of mass states:

No atoms are created or destroyed during a chemical reaction.

This means the total mass of the reactants (the substances you start with) always equals the total mass of the products (the substances formed).

This law was established by Antoine Lavoisier in the 18th century and is one of the most fundamental principles in chemistry.

Why Is Mass Conserved?

In a chemical reaction, the atoms are rearranged — they break apart from one combination and join together in a new combination. The same atoms are present before and after the reaction; they have simply been reorganised.

Since the atoms are the same (and each atom has the same mass), the total mass cannot change.

---

Apparent Changes in Mass