Limiting reactants and theoretical yield
A limiting reactant supplies the smallest reaction extent after its available moles are divided by its stoichiometric coefficient. It therefore sets the maximum ideal amount of product.
This calculator checks element balance for simple neutral formulas before using the coefficients. It can identify co-limiting reactants when entered amounts are present in the exact stoichiometric ratio.
How to calculate the limiting reagent
- Enter a balanced equation: Use -> between sides, + between species, element symbols, integer coefficients, digits for subscripts, and parentheses where needed.
- Enter reactant masses: Provide nonnegative masses in grams for every listed reactant.
- Choose a product: Select which product’s theoretical yield to report.
- Calculate: Review limiting species, theoretical yield, and ideal excess masses.
Formula and variables
Each reactant mass is converted to moles using its formula molar mass, then normalized by its balanced-equation coefficient.
reaction extent ξ = min[nᵢ/νᵢ]; theoretical product moles = ξνproduct- nᵢ — Reactant amount
- Entered mass divided by molar mass (mol)
- νᵢ — Stoichiometric coefficient
- Positive whole-number coefficient in the balanced equation (dimensionless)
- ξ — Reaction extent
- Maximum ideal reaction progress set by limiting reactant (mol reaction)
Hydrogen and oxygen forming water
React 10 g H₂ with 100 g O₂ using 2H₂ + O₂ -> 2H₂O.
- H₂
- 10 g
- O₂
- 100 g
- H₂ extent = (10/2.016)/2 ≈ 2.480 mol reaction
- O₂ extent = (100/31.998)/1 ≈ 3.125 mol reaction
Result: H₂ is limiting; ideal H₂O yield is about 89.36 g, with about 20.64 g O₂ remaining.
The result assumes complete reaction, pure reactants, and no product loss.
Understanding your results
Theoretical yield is an upper stoichiometric limit
Actual isolated yield is commonly lower and must be measured separately.
- Co-limiting reactants are reported together when normalized amounts match within numeric tolerance.
- Excess remaining assumes only the entered reaction consumes that reactant.
- A balanced equation conserves elements but does not prove the reaction occurs or is selective.
- Purity and solution concentration must be converted into actual reactant mass before entry.
Assumptions
- The entered equation is the complete relevant reaction and passes element balance.
- Reactant masses are pure available quantities and reaction proceeds to completion.
- Molar masses from conventional atomic weights are appropriate.
Limitations
- Parser does not support charges, electrons, hydrate dots, phases, fractional coefficients, isotopes, or redox half-reaction notation.
- Does not model equilibrium, kinetics, selectivity, side reactions, purity, solution concentration, or actual yield.
- Element balance checking does not validate charge balance or chemical feasibility.
Common mistakes
- Using an unbalanced equation or changing formula subscripts to balance it.
- Comparing reactant grams directly instead of coefficient-normalized moles.
- Entering solution mass without accounting for solute concentration.
- Calling theoretical yield the expected isolated laboratory yield.
Practical use cases
Stoichiometry coursework
Check limiting-reagent, product-yield, and excess-mass calculations.
Ideal reaction planning
Screen mass relationships after reaction identity, purity, and balanced stoichiometry are established.
Frequently asked questions
How does the calculator find the limiting reactant?
It converts each mass to moles, divides by that reactant’s coefficient, and selects the smallest normalized amount.
Can two reactants both be limiting?
Yes. If they are supplied in the exact stoichiometric ratio, both are consumed together and are reported as co-limiting.
Does a balanced equation guarantee the reaction will occur?
No. Balance is necessary for stoichiometry but does not establish kinetics, thermodynamics, mechanism, or selectivity.
Sources and review
- Writing and Balancing Chemical Equations — OpenStax Chemistry 2e. Accessed 2026-07-13.
- Reaction Yields — OpenStax Chemistry. Accessed 2026-07-13.
Reviewed 2026-07-13.