Chemical equation balancer with an atom check
Type an unbalanced equation and get the smallest whole-number coefficients that make every element match on both sides, with a table that proves it.
Separate the two sides with = or →, and the substances with +. Symbols are case-sensitive: Co is cobalt, CO is carbon monoxide.
Atom check
| Element | Reactants | Products | Balanced |
|---|---|---|---|
| C | 3 | 3 | ✓ |
| H | 8 | 8 | ✓ |
| O | 10 | 10 | ✓ |
Try an example
How to use the balancer
Type the reactants on the left and the products on the right, separated by an equals sign or an arrow (=, -> and → all work). Put a plus sign between substances, as in Fe + O2 = Fe2O3, then press Balance. Coefficients you already typed and state labels such as (aq) or (g) are ignored.
Formulas follow the same rules as the molar mass calculator: brackets such as Ca(OH)2 and hydrates such as CuSO4·5H2O work, and capital letters matter. The result shows the balanced equation and an atom check that counts each element on both sides.
Worked example: iron rusting to iron(III) oxide
Start with Fe + O₂ → Fe₂O₃. Oxygen is the awkward element: each O₂ brings 2 oxygen atoms and each Fe₂O₃ holds 3. The smallest number that both 2 and 3 divide into is 6, so write 3O₂ on the left and 2Fe₂O₃ on the right.
The right side now has 2 × 2 = 4 iron atoms, so put a 4 in front of Fe: 4Fe + 3O₂ → 2Fe₂O₃. Check: 4 iron and 6 oxygen atoms on each side. The coefficients 4, 3 and 2 share no common factor, so this is the simplest form.
How the balancer works
A balanced equation obeys the law of conservation of mass: a reaction rearranges atoms but never creates or destroys them. For each element, the balancer writes one equation saying the atoms on the left equal the atoms on the right, with the unknown coefficients as the variables.
It solves these equations exactly, using fractions rather than rounded decimals, then scales the answer to the smallest whole numbers. If no all-positive answer exists, a formula or a substance is probably wrong. If many answers exist, the equation mixes two independent reactions.
Tips for balancing by hand
Balance elements that appear in only one substance on each side first, and leave hydrogen and oxygen, which often turn up in several places, until last. A polyatomic ion such as SO₄ that stays intact can be balanced as a single unit.
Never change the small numbers inside a formula, because that changes the substance itself: H₂O₂ is hydrogen peroxide, not water. Only the coefficients in front of each formula may change.
FAQ
What does it mean to balance a chemical equation?
It means choosing coefficients, the numbers in front of each formula, so that every element has the same number of atoms on both sides. In 2H₂ + O₂ → 2H₂O there are 4 hydrogen and 2 oxygen atoms on each side.
Why can’t I change the subscripts to balance an equation?
Subscripts define the substance. Changing H₂O to H₂O₂ turns water into hydrogen peroxide, a different compound, so only the coefficients may change.
What is the balanced equation for burning methane?
CH₄ + 2O₂ → CO₂ + 2H₂O. One methane molecule reacts with two oxygen molecules to give one carbon dioxide and two water molecules, with 1 carbon, 4 hydrogen and 4 oxygen atoms on each side.
Can it balance redox and ionic equations?
It balances any equation where only atoms must match, including many redox reactions such as 2KMnO₄ + 16HCl → 2KCl + 2MnCl₂ + 8H₂O + 5Cl₂. It does not handle ionic charges or electrons, so write whole neutral compounds rather than ions.