MolDraw › Chemistry tools › Theoretical Yield Calculator
Theoretical Yield Calculator
Enter a chemical equation and the amounts of your reactants. The calculator balances the equation, finds the limiting reagent and works out the theoretical yield of any product in grams and moles. Add your actual yield to get the percent yield.
How to calculate theoretical yield
- Balance the equation. The calculator does this for you using its equation balancer.
- Convert each reactant to moles: mass ÷ molar mass.
- Find the limiting reagent: divide each reactant's moles by its coefficient. The smallest value is limiting.
- Use the mole ratio: mol product = mol limiting × (product coefficient ÷ limiting coefficient).
- Convert to grams: theoretical yield = mol product × molar mass of product.
Theoretical yield (g) = (mol limiting reagent) × (b/a) × M(product) Percent yield = actual ÷ theoretical × 100%
Worked examples
Aspirin from salicylic acid
2.00 g C₇H₆O₃ (0.01448 mol) with 5.00 g acetic anhydride (0.04898 mol), 1:1 ratio. Salicylic acid is limiting: 0.01448 × 180.16 g/mol
Theoretical yield 2.609 g. If 1.80 g is isolated, the yield is 69.0%
Haber process
28.0 g N₂ (0.9995 mol) + 10.0 g H₂ (4.96 mol). N₂ + 3H₂ → 2NH₃, so N₂ is limiting: 1.999 mol NH₃ × 17.03 g/mol
34.04 g NH₃
Water synthesis
10 g H₂ (4.96 mol) + 64 g O₂ (2.00 mol). 2H₂ + O₂ → 2H₂O, so O₂ is limiting: 4.00 mol H₂O
72.06 g H₂O; 1.94 g H₂ left over
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Open MolDraw editorFrequently asked questions
What is theoretical yield?
Theoretical yield is the maximum amount of product that could form if the limiting reagent reacted completely, with no losses. You calculate it from the balanced equation and the molar masses.
How do you find the limiting reagent?
Convert each reactant to moles and divide by its coefficient in the balanced equation. The reactant with the smallest result runs out first. That is the limiting reagent, and it sets the theoretical yield.
What is the difference between theoretical, actual and percent yield?
Theoretical yield is calculated, actual yield is what you isolate in the lab, and percent yield = actual ÷ theoretical × 100%.
Can percent yield be over 100%?
Not for a pure, dry product. A result above 100% usually means the product still contains solvent or water, or is contaminated, or there was a weighing error.
What if I only know the amount of one reactant?
Enter just that reactant and leave the others blank. They are treated as being in excess, so the reactant you entered is limiting.
Do I need to balance the equation first?
No. Type the unbalanced equation (e.g. C3H8 + O2 -> CO2 + H2O) and the calculator balances it before working out the mole ratios.