Chemical equation balancer

Atoms aren't created or destroyed in a chemical reaction, only rearranged. This is the law of conservation of mass, and it's why the number of atoms of each element must be the same on both sides. You balance an equation by changing the numbers in front of formulas (coefficients), never the small numbers inside them, because changing a subscript changes the substance: H₂O is water, H₂O₂ is hydrogen peroxide.

Take Fe + O₂ → Fe₂O₃:

1. Count atoms on each side. Left: 1 Fe, 2 O. Right: 2 Fe, 3 O.
2. Balance the element in the fewest formulas, saving O and H for last. Put 2 in front of Fe: 2Fe + O₂ → Fe₂O₃.
3. Balance oxygen. 2 on the left, 3 on the right. The lowest common multiple is 6: 2Fe + 3O₂ → 2Fe₂O₃.
4. Re-check iron. Now 4 on the right, so 4Fe + 3O₂ → 2Fe₂O₃.
5. Check every element and make sure the coefficients can't be divided further.

Hydrocarbons burn in plenty of oxygen to make carbon dioxide and water. Balance carbon, then hydrogen, then oxygen last:

• CH₄ + 2O₂ → CO₂ + 2H₂O
• C₃H₈ + 5O₂ → 3CO₂ + 4H₂O

If oxygen ends up needing a half (as with ethane), double everything: 2C₂H₆ + 7O₂ → 4CO₂ + 6H₂O.

It writes one equation for each element (atoms on the left = atoms on the right) and solves them together with exact fractions, then scales the answer to the smallest whole numbers. That means it never guesses, and it tells you when an equation can't be balanced: usually a typo in a formula or a substance on the wrong side. It also warns you when an equation could balance in more than one way, which means it's really two reactions written together.

• Capitals matter. Co is cobalt; CO is carbon monoxide. Every element symbol starts with a capital letter.
• Brackets: Ca(OH)2 means one calcium, two oxygens and two hydrogens.
• Hydrates: use a dot, as in CuSO4.5H2O.
• Ions: charged formulas aren't supported yet; write the full neutral compounds.

For practice balancing on your own, try our balancing equations questions or read the balancing chemical equations guide.