How stoichiometry works
In a balanced equation, coefficients are mole ratios: 2 H₂ + O₂ → 2 H₂O means 2 moles of H₂ react with 1 mole of O₂ to make 2 moles of H₂O. Any known amount (grams or moles) of any species scales every other species by its coefficient ratio: molesₓ = moles_known × (coeffₓ ÷ coeff_known).
Using the calculator
- Enter your balanced equation as species lines: name, coefficient, molar mass. The calculator does not balance equations for you — that's the step you must verify (the coefficients must already be balanced).
- Pick the known species and enter its amount (grams or moles). Everything else is computed: moles and grams for every species.
- Find the limiting reagent by trying each reactant as the known amount and seeing which produces the least product — the smallest product amount is the theoretical yield.
- Gases: if you know volume at STP, 1 mol ≈ 22.4 L; at room conditions use the ideal gas law instead.
Example
Species: H₂ (2, 2.02), O₂ (1, 32.00), H₂O (2, 18.02). Known: 4 g H₂ = 1.98 mol. H₂O moles = 1.98 × (2÷2) = 1.98 mol = 35.7 g H₂O; O₂ needed = 1.98 × (1÷2) = 0.99 mol = 31.7 g. The calculator does this for every species at once.