Percent Yield Calculator
This percent yield calculator shows what percentage of the theoretically possible product was actually obtained. Example: 8.5 g obtained from 10 g theoretical gives 85%.
Example: Theoretical yield: Enter directly · Actual yield 8.5 g · Theoretical yield 10 g → Result: Percent yield = 85 % (8.5 g of 10 g theoretical). Source: Wikipedia – Yield (chemistry): percent yield = actual / theoretical × 100 %. Updated: .
How it is calculated
The percent yield compares the amount of product actually obtained with the amount that would form in a complete, loss-free reaction. It measures how efficient a synthesis was and is almost always reported in the lab.
Formulas
Percent yield = actual yield / theoretical yield · 100%. The theoretical yield follows from the limiting reagent, the starting material used up first: m_theo = (m_reagent / M_reagent) · (ν_product / ν_reagent) · M_product. Here ν are the coefficients of the balanced equation.
Worked example
When heating calcium carbonate (CaCO₃ → CaO + CO₂, both coefficients 1), 10 g of CaCO₃ (M = 100.09 g/mol) is used. That is 0.0999 mol, which would theoretically give 0.0999 mol of CaO (M = 56.08 g/mol), or 5.603 g. If you actually obtain 4.8 g, the yield is 4.8 / 5.603 · 100% ≈ 85.67%. If the theoretical yield of 10 g is entered directly and 8.5 g forms, the result is 85%.
- The equation must be balanced, otherwise the coefficients are wrong.
- With several reagents, the limiting one has the smallest amount of substance divided by its coefficient.
- Yields above 100% point to errors, such as solvent left in the product.
Frequently asked questions
How do you calculate percent yield?
Divide the actual yield by the theoretical yield and multiply by 100. Example: 8.5 g / 10 g · 100% = 85%.
How do you find the theoretical yield?
From the amount of the limiting reagent, the ratio of coefficients and the molar mass of the product. In the example, 10 g of CaCO₃ theoretically gives 5.603 g of CaO.
Why is the yield usually below 100%?
Because of incomplete reaction, by-products and losses when isolating and purifying the product.
Sources and legal basis
- Wikipedia – Yield (chemistry): percent yield = actual / theoretical × 100 %
- IUPAC – Atomgewichte (Ca 40,078, C 12,011, O 15,999 → CaCO₃ 100,09; CaO 56,08 g/mol)
- Brown/LeMay/Bursten, Chemistry: The Central Science, Kap. „Limiting reactants and theoretical yields“ (siehe Wikipedia – Limiting reagent)
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