Balancing Chemical Equations

Balancing a chemical equation means adjusting only coefficients, never subscripts, until every element's atom count matches on both sides.

Propane's combustion, C3H8 + O2 → CO2 + H2O, is balanced by first matching carbon with a coefficient of 3 on CO2, then hydrogen with a coefficient of 4 on H2O, which fixes ten oxygen atoms on the product side. Placing a coefficient of 5 on O2 supplies exactly ten oxygen atoms on the reactant side, giving the balanced equation C3H8 + 5O2 → 3CO2 + 4H2O, checked by counting three carbon, eight hydrogen, and ten oxygen atoms on each side.