Massenerhaltungs

Massenerhaltung, or the conservation of mass, is the principle that in a closed system the total mass remains constant over time. In many physical and chemical processes, the sum of the masses of all substances entering a system equals the sum of the masses of all substances leaving it, provided no material crosses the system boundaries.

Historically, the law was established by Antoine Lavoisier in the late 18th century, based on experiments showing that chemical reactions do not create or destroy mass; reactants are transformed into products with equal total mass.

In chemistry, mass conservation underpins the balancing of chemical equations and the stoichiometry of reactions. In physics and engineering, mass balances are used to model reactors, separators, and flow processes. For fluids, the mass conservation is expressed by the continuity principle, requiring that mass flow is preserved as it moves through space.

Mass balance in open systems uses the concept of a control volume: inflow plus generation minus outflow minus consumption equals accumulation. This framework applies to batch and continuous processes, including chemical reactors, distillation columns, and environmental systems.

Limitations and extensions: In relativistic contexts, mass can be converted to energy and vice versa; the general law is conservation of mass–energy. In ordinary chemical and mechanical processes, mass is conserved to a high degree of accuracy, with small differences attributable to measurement limits or to energy changes that are accounted as energy rather than mass. In nuclear reactions, a small mass defect appears as released energy, illustrating the mass–energy connection.

Overall, the conservation of mass remains a foundational principle in classical science, informing analysis and design across chemistry, engineering, and physics.