A law stating that the total magnitude of a certain physical property of a system, such as its mass, energy, or charge, remain unchanged even though there may be exchanges of that property between components of the system. For example, imagine a table with a bottle of salt solution (NaCl), a bottle of silver nitrate solution (AgNO3), and a beaker standing on it. The mass of this table and its contents will not change even when some of the contents of the bottles are poured into the beaker. As a result of the reaction between the chemicals two new substances (silver chloride and sodium nitrate) will appear in the beaker:NaCl+AgNO3 → AgCl+NaNO3,but the total mass of the table and its contents will not change. This conservation of mass is a law of wide and general applicability, which is true for the universe as a whole, provided that the universe can be considered a closed system (nothing escaping from it, nothing being added to it). According to Einstein's mass-energy relationship, every quantity of energy (E) has a mass (m), which is given by E/c2, where c is the speed of light. Therefore if mass is conserved, the law of conservation of energy must be of equally wide application.
NaCl+AgNO3 → AgCl+NaNO3
Subjects: Chemistry — Physics.