Balance: H₂ + O₂ → H₂O.

2 H₂ + O₂ → 2 H₂O. Left: 4H, 2O. Right: 4H, 2O. ✓.

Balance: Fe + O₂ → Fe₂O₃.

4 Fe + 3 O₂ → 2 Fe₂O₃. Left: 4Fe, 6O. Right: 4Fe, 6O. ✓.

Balance: C₃H₈ + O₂ → CO₂ + H₂O (combustion of propane).

C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O. Left: 3C, 8H, 10O. Right: 3C, 8H, 10O. ✓.

Balance: KMnO₄ + HCl → KCl + MnCl₂ + H₂O + Cl₂ (redox reaction).

2 KMnO₄ + 16 HCl → 2 KCl + 2 MnCl₂ + 8 H₂O + 5 Cl₂. This is an oxidation-reduction reaction requiring careful electron balance.

Free~15 min

Balancing Chemical Equations

Conservation of mass through coefficient adjustment

How it works

Chemical equations represent reactions where atoms rearrange but are never created or destroyed (Law of Conservation of Mass, Lavoisier 1789). Balancing means finding the smallest set of integer coefficients so that every element has equal atom counts on both sides. Strategy: balance metals first, then nonmetals, then hydrogen, and oxygen last. For combustion reactions, balance C first, then H, then O. Redox reactions may require half-reaction balancing. A balanced equation is the foundation of stoichiometry — it tells you the mole ratios needed for quantitative calculations.

Step-by-step

Select a reaction from the dropdown.
Use the + and − buttons (or click the coefficient) to adjust each coefficient.
The atom inventory panel shows real-time counts for each element on both sides.
When all elements match, the equation turns green and you earn a ✓.
Try all 8 reactions, from simple synthesis to combustion and redox.

Key formulas

$\text{Reactants (atoms)} = \text{Products (atoms)} \quad \text{(Conservation of Mass)}$ In a balanced equation, the number of atoms of each element is equal on both sides
$a\,\text{A} + b\,\text{B} \rightarrow c\,\text{C} + d\,\text{D}$ Coefficients a, b, c, d are the smallest whole numbers that balance all elements

Frequently asked questions

Balance: H₂ + O₂ → H₂O.: 2 H₂ + O₂ → 2 H₂O. Left: 4H, 2O. Right: 4H, 2O. ✓.
Balance: Fe + O₂ → Fe₂O₃.: 4 Fe + 3 O₂ → 2 Fe₂O₃. Left: 4Fe, 6O. Right: 4Fe, 6O. ✓.
Balance: C₃H₈ + O₂ → CO₂ + H₂O (combustion of propane).: C₃H₈ + 5 O₂ → 3 CO₂ + 4 H₂O. Left: 3C, 8H, 10O. Right: 3C, 8H, 10O. ✓.
Balance: KMnO₄ + HCl → KCl + MnCl₂ + H₂O + Cl₂ (redox reaction).: 2 KMnO₄ + 16 HCl → 2 KCl + 2 MnCl₂ + 8 H₂O + 5 Cl₂. This is an oxidation-reduction reaction requiring careful electron balance.