Chemical Equation Balancer

It divides each reactant's available moles by its own stoichiometric coefficient, producing a "moles of reaction" ratio for each. Whichever reactant has the smaller ratio is the Limiting Reactant, because it will be fully consumed first as the reaction proceeds -- the other reactant has enough on hand to keep reacting past that point, so some of it is left over as Excess Reactant once the limiting reactant runs out.

Product 1 Produced is set entirely by the limiting reactant's ratio and Product 1's own coefficient. If Reactant 1 is the limiting reactant, Reactant 2 has moles to spare -- some of it becomes Excess Reactant, but it doesn't constrain how much product forms. Reactant 2 only starts moving Product 1 Produced once you change its coefficient or moles enough that it becomes the NEW limiting reactant instead of Reactant 1. This calculator verifies that switch-over behavior directly against the engine across the full input range, not just near the default values.

Each product's yield is calculated independently from the same limiting-reactant ratio: Product 1 Produced = limiting ratio × Product 1 Coefficient, and Product 2 Produced = limiting ratio × Product 2 Coefficient. Product 2's coefficient only appears in that second equation, so it has no path to influence Product 1's result -- changing it can only ever change how much of Product 2 forms.

It's the moles of the non-limiting reactant that remain unreacted once the reaction has consumed all of the limiting reactant and gone to completion. In a real lab or industrial process, this is the material you'd need to recover, recycle, or safely dispose of -- and a large Excess Reactant value relative to what you started with often signals that your reactant ratio doesn't match the balanced equation's stoichiometry.

Yes -- this calculator performs the stoichiometry math from coefficients you supply, but it does not derive a balanced equation from unbalanced reactant and product formulas. Enter the coefficients exactly as they appear in your already-balanced chemical equation (for example, 2 and 1 for 2H2 + O2 → 2H2O), then supply how many moles of each reactant you actually have on hand.