Conservation of mass

The mass conservation law (Lomonosov Lavoisier law) is a conservation law in the field of chemistry, which states that the mass does not change appreciably in chemical reactions.

Physics

The sum of the ( rest) mass of the particles involved is not conserved in all processes. The pair annihilation, wherein an electron and a positron annihilated and two photons are generated, the mass is zero, is a simple counter-example.

When nuclear fission and nuclear fusion reactions in some of the so-called mass defect occurs: The sum of the masses of the resulting particles is less than the sum of the initial core masses. Since the rest energy can be read off at the ground, the resulting particles at rest less energy than the initial particles have. This energy difference is converted by nuclear fission or nuclear fusion in heat and radiation; provided that the total energy is conserved, but not the ( rest) mass.

Chemistry

1748 postulated Mikhail Lomonosov, the mass conservation law. In a chemical reaction in a closed system the sum of the mass of the reactants is equal to the sum of the mass of products: phrased it in 1789 by Antoine Laurent de Lavoisier was. Since before the discovery of oxygen (1772 or 1774) for burns this law could not be applied, the phlogiston theory was developed as an auxiliary construction.

Illustration of the phlogiston theory

• If you burn coal, ash remains. The ash is lighter than the raw material coal.
• When strongly heated a piece of iron wool, creating a gray - blue solid. It is significantly heavier than the starting material iron wool.

What was not taken into account in such a view, is that not all of the reaction products were taken into account. When coal burns, carbon dioxide is produced (gas). Also, this gas has a mass.

When steel wool is heated, it combines with the oxygen in the surrounding air. Also, the oxygen has a mass. When performing these reactions in a closed vessel, it will be noted that the mass of material in the vessel remains constant.

The energy released in exothermic chemical reactions energy is liberated binding energy of the electrons. In fact, the mass does not remain the same: The mass defect of an exothermic reaction, the products are in fact easier than the educts, although this effect is very small. When burning a kilogram of coal ( calorific value angenommerner about 35 MJ) "disappear" due to the mass defect nearly 0.4 micrograms.