Start typing an element or compound and pick it from the list — or load one of the ready-made reactions below. It writes the balanced equation and explains every step.
Ready-made reactions
Reactants (what you start with)
Iron
Oxygen gas
↓
Products (what you end up with)
Iron(III) oxide (rust)
Balanced equation
4Fe + 3O2 → 2Fe2O3
Iron corrodes only when air and water are both present.
Atom
Left
Right
Match
Fe
4
4
✓
O
6
6
✓
1 · Write the skeleton equation
Put the reactants on the left and the products on the right, joined by an arrow:
Fe + O2 → Fe2O3
Never change a formula to balance — only the numbers in front may change.
2 · Count each element on both sides
Fe (1 left vs 2 right) and O (2 left vs 3 right) do not match, so the skeleton is not balanced yet.
3 · Add coefficients
Multiply whole formula units until each element matches: put 4 in front of Fe, 3 in front of O2 and 2 in front of Fe2O3. Every other substance stays at 1.
4 · Balanced equation
4Fe + 3O2 → 2Fe2O3
5 · Check it
Fe: 4 = 4 · O: 6 = 6
Mass check: 319.374 g/mol of reactants = 319.374 g/mol of products, so mass is conserved.
Classes 6–8
First measurements, first compound formulas and the language of chemistry.