The Law of Conservation of Mass
Chemical equations must be balanced to satisfy the Law of Conservation of Mass. This fundamental scientific principle states that matter cannot be created or destroyed in an isolated system. For a chemical reaction, this means the total number and type of atoms going into the reaction (reactants) must be equal to the total number and type of atoms coming out (products).
Section 2: Accounting for Every Atom
Balancing an equation is essentially a process of atomic bookkeeping. By adjusting the stoichiometric coefficients—the numbers placed in front of chemical formulas—we ensure that the atom count for each element is identical on both sides of the reaction arrow. This demonstrates that atoms are only rearranged into new molecules, not created or lost during the reaction.
Section 3: A Practical Example with Water
Consider the formation of water from hydrogen and oxygen: H₂ + O₂ → H₂O. This initial equation is unbalanced because there are two oxygen atoms on the reactant side but only one on the product side. The correctly balanced equation is 2H₂ + O₂ → 2H₂O. Now, both sides have four hydrogen atoms and two oxygen atoms, perfectly upholding the conservation of mass.
Section 4: Importance in Calculations
A balanced chemical equation is the foundation of stoichiometry, the branch of chemistry that deals with the quantitative relationships of reactants and products. It allows chemists to accurately predict the amount of product that will be formed from a certain amount of reactants, identify the limiting reactant, and calculate the theoretical yield of a reaction. Without a balanced equation, these essential calculations would be impossible.