The law of conservation of mass asserts that in a chemical reaction, the total mass of the reactants is equal to the total mass of the products.

More specifically, the law of conservation of mass, often referred to as the principle of mass conservation, is a foundational concept in the field of chemistry. This principle was first articulated by Antoine Lavoisier in the late 18th century. It states that matter cannot be created or destroyed within an isolated system. In the context of a chemical reaction, this implies that the total mass of the substances involved remains constant, irrespective of the identities of the substances, the processes through which they are transformed, or the resulting products.

For instance, when hydrogen gas reacts with oxygen gas to form water, the total mass of the hydrogen and oxygen initially present will equal the total mass of the resulting water. This occurs because the hydrogen and oxygen atoms are not annihilated or generated during the reaction; instead, they are merely rearranged to create water molecules.

This principle plays a critical role in balancing chemical equations. In a balanced chemical equation, the number of atoms of each element on the reactants’ side must match the number of atoms of that element on the products’ side. This requirement reflects the law of conservation of mass, which dictates that the total mass before and after the reaction remains unchanged.

It is essential to recognize that this law is applicable strictly to closed systems, where no matter can enter or exit. In contrast, in an open system, the mass of the reactants and products may differ due to the exchange of matter with the environment.

In summary, the law of conservation of mass is a fundamental principle in chemistry that governs the rearrangement of atoms during chemical reactions. It guarantees that matter is neither lost nor gained during a reaction, thereby maintaining a constant total mass.