Complete a chemical reaction

Know the reactants but not the products yet? Enter only what reacts. For a recognized common case, the tool suggests the products and then balances the equation automatically.

Tool→?

Simplest example: enter H2 + O2. The tool recognizes a common hydrogen–oxygen reaction, suggests H2O, then balances it as 2 H₂ + O₂ → 2 H₂O.

Reactants only

Enter only the species present at the start, separated by +. Do not enter an arrow or products.

Worked example 1

H₂ + O₂: from two reactants to water

1. What you enter: H2 + O2. You provide only the reactants.

2. Suggested product: H2O, water. In this common classroom case, hydrogen burns in oxygen.

3. Why balancing is still needed: in H2 + O2 → H2O, there are 2 oxygen atoms on the left but only 1 on the right.

4. Result: 2 H₂ + O₂ → 2 H₂O. Both sides now contain 4 H atoms and 2 O atoms.

Worked example 2

CH₄ + O₂: methane combustion

Enter CH4 + O2. For complete combustion with sufficient oxygen, the expected products are CO2 + H2O. The balanced equation is CH₄ + 2 O₂ → CO₂ + 2 H₂O.

The word “complete” matters: with insufficient oxygen, combustion can produce carbon monoxide. This is why the tool states assumptions and refuses some ambiguous cases.

Worked example 3

HCl + NaOH: acid–base neutralization

Enter HCl + NaOH. In this common aqueous reaction, the products are sodium chloride and water: HCl + NaOH → NaCl + H₂O. Here every coefficient is already 1.

What this tool can — and cannot — infer

Reactants alone do not always determine one unique product. Temperature, pressure, solvent, concentration, catalyst and proportions can change the reaction. The tool therefore does not claim to “predict all chemistry”: it recognizes common classroom reactions and sufficiently reliable patterns. When a case is ambiguous, it returns no product rather than inventing one.

If you already know the products and only need the coefficients, use Balance a chemical equation.