Chemistry and laboratory
Limiting reagent and percent yield calculator
Find the limiting reagent, theoretical yield, leftover excess and percent yield from an equation (balanced for you) and reactant amounts.
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Result
- Limiting reagent
- CO
- Theoretical yield of Fe
- 66.5 g
- Percent yield
- 82.8 %
- Amount of Fe
- 1.19 mol
- Balanced equation
- Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂
Working
- For each reactant: moles given ÷ its coefficient. The smallest value is the extent of reaction ξ, and that reactant is limiting.
- ξ = 0.595026 mol, so Fe: 2 × ξ × M = 66.5 g
- Percent yield = actual ÷ theoretical × 100 = 55.0 g ÷ 66.4584 g × 100 = 82.7585 %
| Reactant | Given | Moles | Coefficient | Moles ÷ coefficient | Moles used | Left over |
|---|---|---|---|---|---|---|
| Fe₂O₃ | 100.0 g | 0.626 | 1 | 0.626 | 0.595 | 4.98 g |
| CO | 50.0 g | 1.79 | 3 | 0.595 | 1.79 | 0 (used up) |
| Product | Moles | Mass |
|---|---|---|
| Fe | 1.19 | 66.5 g |
| CO₂ | 1.79 | 78.6 g |
- Amounts without a unit are read as grams. Reactants you leave out are assumed to be in excess.
- Rounded to 3 significant figures.
Method and limits
Enter the reaction and the amounts of the reactants you have. The tool balances the equation, converts each amount to moles and finds which reactant runs out first.
Method
- Balance the equation (the same exact method as the equation balancer).
- Convert each reactant to moles: n = m ÷ M.
- Divide each by its coefficient. The smallest quotient is the extent of reaction ξ, and that reactant is limiting.
- Theoretical yield of a product = its coefficient × ξ × its molar mass. Leftover excess = (moles given − coefficient × ξ) × M.
- Percent yield = actual yield ÷ theoretical yield × 100 %.
Molar masses use CIAAW 2024 abridged atomic weights. Answers keep the significant figures of the least precise number you enter (at least 3, at most 6); counts and coefficients are exact and do not limit precision.
Limits
The theoretical yield assumes the reaction goes to completion with no side reactions. A percent yield above 100 % usually means the product is wet or impure. Reactants you do not list are assumed to be in excess.
Worked example
Fe₂O₃ + 3 CO → 2 Fe + 3 CO₂ with 100.0 g Fe₂O₃ (0.6262 mol) and 50.0 g CO (1.785 mol): CO gives 1.785 ÷ 3 = 0.595 mol of reaction, less than Fe₂O₃’s 0.626, so CO is limiting. Iron: 2 × 0.595 mol × 55.845 g/mol = 66.5 g. Obtaining 55.0 g is an 82.8 % yield.
References
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