* Atoms are not created or destroyed: The fundamental principle of the conservation of mass states that matter cannot be created or destroyed in ordinary chemical and physical changes. This means the total number of atoms of each element on the reactant side (the starting materials) must equal the total number of atoms of each element on the product side (the substances formed).
* Rearrangement, not disappearance: During a chemical reaction, atoms are not lost or gained. Instead, they simply rearrange themselves to form new molecules or compounds. The atoms themselves remain unchanged.
* Balancing chemical equations: We use balanced chemical equations to represent this principle. The coefficients in front of each chemical formula indicate the number of molecules or moles of each substance involved. By balancing the equation, we ensure that the same number of atoms of each element is present on both sides of the equation.
Example:
Consider the combustion of methane (CH₄):
CH₄ + 2O₂ → CO₂ + 2H₂O
* Reactants: 1 carbon (C), 4 hydrogen (H), and 4 oxygen (O) atoms.
* Products: 1 carbon (C), 4 hydrogen (H), and 4 oxygen (O) atoms.
The atoms are simply rearranged, with the carbon and hydrogen atoms from methane combining with oxygen atoms from the air to form carbon dioxide and water. The total number of each type of atom remains the same, demonstrating the conservation of mass.
