About the Law of Conservation of Mass

Considerations

The Law of Conservation of Mass applies only to a closed system, that is, a system which no energy or matter can leave or enter. In nature, no system is truly closed as nothing in nature is totally isolated from the outside environment and energy or matter may be transferred in many forms, including chemical, heat and light. Because a closed system is purely theoretical, it may seem to the casual observer as though matter is being destroyed when in fact it has just changed from one form to another, such as from a solid to a gas.

An early version of the Law of Conservation of Mass was stated by Roman poet Lucretius, who said, "Things cannot be born from nothing." Although Lucretius was expressing a philosophical idea and not necessarily a physics concept, he laid a foundation for future scientists to build upon. The Law of Conservation of Mass was first stated as a physical theory by Russian scientist Mikhail Lomonosov in 1748. This theory was later reiterated and confirmed by French scientist Antoine Lavoisier in 1789. Lavoisier verified his theory in practice by carrying out a number of carefully measured experiments in which he reacted tin and lead with oxygen.

The Law of Conservation of Mass is often applied to basic chemical reactions to explain what happens on an atomic level during a reaction--that every atom present at the start of the reaction is still present at the end of the reaction. A simple example of this is the reaction of hydrogen with oxygen to form water. When the Law of Conservation of Mass is applied to this reaction, the reaction balances in a way to demonstrate that two hydrogen atoms must be present for every one oxygen atom in order to yield one molecule of water. Therefore the reaction is written as 2H + O ----> H2O, demonstrating that every atom involved in the reaction is accounted for.

The conservation laws are a set of scientific laws that have developed out of the Law of Conservation of Mass. These laws unite the physical sciences and explain the properties of a variety of movement and energy. For example, the Law of Conservation of Electrical Charge states that the total charge in an isolated system remains the same. There are several other laws of conservation including the Law of Conservation of Momentum and the Law of Conservation of Parity.

Einstein's theory of relativity forever changed the definition of the Law of Conservation of Mass. Prior to Einstein's famous theory, there were two separate laws to describe the conservation of mass and the conservation of energy. Einstein showed that matter and energy can be transformed into one another and revolutionized the way scientists understand matter and energy. Subsequently, the separate laws of energy and mass conservation have been combined into one law: the Law of Conservation of Mass-Energy, which holds that neither mass nor energy can be created or destroyed.