Using the model
Symbols, assumptions and limitations
Enter a balanced reaction or select a preset. Stoichiometric coefficients provide mole ratios, never mass ratios. The model assumes pure substances and complete reaction according to the displayed equation; side reactions, equilibrium, impurities, and measurement uncertainty are excluded.
Worked examples
See the method in practice
Water formation
For 2H₂ + O₂ → 2H₂O, 4.032 g H₂ reacts exactly with 31.998 g O₂ to form about 36.030 g H₂O.
Limiting ammonia reagent
For N₂ + 3H₂ → 2NH₃, comparing n/ν for both reactants identifies which supply runs out first and how much excess remains.
Questions
Frequently asked
Why must the equation be balanced first?
Only a balanced equation conserves atoms and supplies valid mole ratios between reactants and products.
What is the limiting reactant?
It is the reactant with the smallest available amount divided by its stoichiometric coefficient. It fixes the maximum reaction extent and theoretical yield.
Can percent yield exceed 100%?
An apparent value above 100% usually indicates wet or impure product, an incorrect reaction model, or measurement error; the calculator reports it but it is a warning sign.
Sources & review
Equations and examples are checked against the references below. Results are educational and should be independently verified for safety-critical work.
OpenStax Chemistry — Reaction Stoichiometry OpenStax Chemistry — Reaction YieldsWritten by the STEM Hub editorial team · Reviewed August 11, 2026 · Review methodology