How to Balance Chemical Equations: 5 Methods That Work

Balanced chemical equations obey the Law of Conservation of Mass — matter is neither created nor destroyed in a chemical reaction. Every atom present in the reactants must appear in the products. Coefficients (the numbers in front of formulas) are the only things you can change when balancing. Never alter subscripts — changing H2O to H2O2 changes the substance entirely.

The most common method for simple equations. Look at each element, count atoms on each side, and adjust coefficients to make them equal. Start with elements that appear in only one reactant and one product. Save oxygen and hydrogen for last (they often appear in multiple compounds). Example: __Fe + __O2 → __Fe2O3. Start with Fe: 2 Fe on the right, so put 2 in front of Fe. Now balance O: 3 on the right, 2 on the left. Use 3 for O2 and multiply Fe2O3 by 2: 4Fe + 3O2 → 2Fe2O3.

When an element has an odd number on one side and an even number on the other, multiply the odd side by 2 to make it even, then balance from there. Example: __C2H6 + __O2 → __CO2 + __H2O. Carbon: 2 on left, 1 on right → put 2 in front of CO2. Hydrogen: 6 on left, 2 on right → put 3 in front of H2O. Oxygen: 4 + 3 = 7 on right (odd), 2 on left (even). Multiply everything by 2: 2C2H6 + 7O2 → 4CO2 + 6H2O. Check: C: 4=4, H: 12=12, O: 14=14.

For complex equations, assign variables to each coefficient and set up a system of equations. Example: __aCH4 + __bO2 → __cCO2 + __dH2O. Carbon: a = c. Hydrogen: 4a = 2d, so d = 2a. Oxygen: 2b = 2c + d = 2a + 2a = 4a, so b = 2a. Set a = 1: b = 2, c = 1, d = 2. Answer: CH4 + 2O2 → CO2 + 2H2O. This method always works and is especially useful for equations with 4+ compounds.

When polyatomic ions appear intact on both sides, treat them as a single unit rather than balancing each element separately. Example: __Ca(OH)2 + __H3PO4 → __Ca3(PO4)2 + __H2O. Treat PO4 as a unit: 1 on left, 2 on right → put 2 in front of H3PO4. Treat Ca: 1 on left, 3 on right → put 3 in front of Ca(OH)2. Now count H and balance H2O: 6 (from 3Ca(OH)2) + 6 (from 2H3PO4) = 12H → 6H2O. Answer: 3Ca(OH)2 + 2H3PO4 → Ca3(PO4)2 + 6H2O.

For redox (oxidation-reduction) reactions, split the equation into two half-reactions — one for oxidation and one for reduction. Balance each half-reaction separately for atoms and charge, then combine them. This method is essential for electrochemistry and is covered in detail in our redox-balancing practice problems. ChemistryIQ can balance equations from a photo using any of these methods — snap a picture of your unbalanced equation for instant step-by-step solutions.

Balance metals first, then nonmetals, then hydrogen, then oxygen last. For combustion reactions, always balance C first, H second, O last. If you get fractions, multiply all coefficients by the denominator to get whole numbers. Always verify by counting every atom on both sides after balancing. For practice, start with simple equations and gradually increase complexity.