How to balance a chemical equation
- Type the reactants and products with = or -> between them, and + between formulas: C3H8 + O2 = CO2 + H2O. Coefficients you type are ignored and worked out again.
- For ions, add the charge after the formula: Fe3+, Cl-, SO4^2- or SO4{2-}. Use e- for electrons in half-equations.
- Read the balanced equation and the table that counts every element on both sides. Click a line to copy it with subscripts or as plain text.
Why equations must balance
Atoms are not created or destroyed in a chemical reaction, so every atom on the left must turn up on the right. Burning propane, C₃H₈ + O₂ → CO₂ + H₂O, needs five oxygen molecules for every propane molecule: C₃H₈ + 5O₂ → 3CO₂ + 4H₂O, with 3 carbon, 8 hydrogen and 10 oxygen atoms on each side.
The coefficients are also the mole ratios you use in stoichiometry: one mole of propane needs five moles of oxygen and gives three moles of carbon dioxide. Combine them with the molar mass calculator to turn moles into grams.
Writing formulas the balancer understands
- Element symbols start with a capital letter: Co is cobalt, CO is carbon monoxide.
- Brackets multiply: Ca(OH)2, Fe2(SO4)3, K4[Fe(CN)6].
- Hydrates: CuSO4·5H2O or CuSO4*5H2O.
- Charges go at the end: Na+, Fe3+, SO4^2-, SO4{2-}. For a polyatomic ion with a charge above 1, use ^ or braces so SO42- isn’t read as 42 oxygen atoms.