Here's why:
* Atoms are not created or destroyed: Chemical reactions involve the rearrangement of atoms, not the creation or destruction of them. The atoms present in the reactants are simply reorganized to form new products.
* Mass is a property of matter: The mass of a substance is determined by the number of atoms it contains. Since the number of atoms remains constant, the total mass must also remain constant.
Example:
Consider the reaction of hydrogen gas (H2) with oxygen gas (O2) to form water (H2O):
2H2 + O2 → 2H2O
* Reactants: 2 molecules of H2 (4 hydrogen atoms) and 1 molecule of O2 (2 oxygen atoms)
* Products: 2 molecules of H2O (4 hydrogen atoms and 2 oxygen atoms)
Notice that the number of atoms of each element is the same on both sides of the equation. Therefore, the total mass of the reactants equals the total mass of the products.
Important Note:
* The Law of Conservation of Mass applies to closed systems, meaning no matter can enter or leave.
* Nuclear reactions, which involve changes to the nucleus of an atom, are an exception to this law. In these reactions, some mass can be converted to energy and vice versa, as described by Einstein's famous equation E=mc².
