Theoretical Yield Calculator
Calculate the theoretical yield of a chemical reaction using limiting reactant mass, molar masses, and stoichiometric ratios.
What the theoretical yield calculator does
The theoretical yield calculator predicts the maximum mass of product a reaction can form from a given amount of limiting reactant. Enter the mass of the limiting reactant, its molar mass, the molar mass of the product, and the stoichiometric ratio of product to reactant from the balanced equation. Press Calculate to get the theoretical yield in grams, along with the moles of reactant and product used in the working.
How the calculation works
- Moles of limiting reactant = mass ÷ molar mass of reactant
- Moles of product = moles of reactant × stoichiometric ratio (product coefficient ÷ reactant coefficient)
- Theoretical yield = moles of product × molar mass of product
With the default values, 10 g of NaCl (58.44 g/mol) at a 1:1 ratio to a product of molar mass 18.02 g/mol gives 0.1711 mol of reactant, 0.1711 mol of product and a yield of 3.08 g.
Worked examples
Combustion of methane: CH₄ + 2 O₂ → CO₂ + 2 H₂O. 16.0 g of methane (16.04 g/mol) with excess oxygen. Moles CH₄ = 0.998. The ratio of H₂O to CH₄ is 2, so moles of water = 1.995 and the theoretical yield of water = 1.995 × 18.02 = 35.9 g. Enter 16, 16.04, 18.02 and 2.
Precipitation: AgNO₃ + NaCl → AgCl + NaNO₃. 5.00 g of AgNO₃ (169.87 g/mol) with excess NaCl. Moles = 0.02943; ratio 1; AgCl molar mass 143.32; yield = 4.22 g.
Thermal decomposition: 2 KClO₃ → 2 KCl + 3 O₂. 24.5 g of KClO₃ (122.55 g/mol). Moles = 0.1999; ratio of O₂ to KClO₃ is 3/2 = 1.5; moles O₂ = 0.2999; yield = 0.2999 × 32.00 = 9.60 g. Enter the ratio as 1.5.
Aspirin synthesis. 2.00 g of salicylic acid (138.12 g/mol) with excess acetic anhydride, ratio 1, product acetylsalicylic acid (180.16 g/mol). Moles = 0.01448; yield = 2.61 g. A student who isolates 1.95 g has a percent yield of 74.7%.
Finding the limiting reactant first
The calculator needs the limiting reactant, the one that runs out first. To identify it, divide the moles of each reactant by its coefficient in the balanced equation; the smallest quotient marks the limiting reactant. For 10.0 g of Al (0.371 mol) and 30.0 g of Cl₂ (0.423 mol) in 2 Al + 3 Cl₂ → 2 AlCl₃: Al gives 0.371/2 = 0.185, Cl₂ gives 0.423/3 = 0.141, so chlorine is limiting. Enter chlorine’s mass and molar mass, with a ratio of 2/3 = 0.667 for AlCl₃. The stoichiometry calculator and moles calculator handle these preliminary steps, and the molar mass calculator supplies the molar masses.
From theoretical to actual yield
Real reactions rarely reach the theoretical figure. Incomplete reaction, side products, losses during transfer, filtration and recrystallisation, and impure starting materials all reduce the amount isolated. Percent yield = actual ÷ theoretical × 100 is the standard measure; the percent yield calculator computes it. Yields above 100% indicate that the product is wet, contains solvent, or is contaminated.
Common mistakes
- Entering the ratio the wrong way round. It is the product coefficient divided by the reactant coefficient. For 2 H₂ + O₂ → 2 H₂O with O₂ limiting, the ratio is 2.
- Using the excess reactant. The yield is set by the limiting reactant only.
- Unbalanced equations. The ratio is meaningless unless the equation is balanced first.
- Molar mass of a hydrate. If the reactant is weighed as a hydrate, use the hydrate’s molar mass.
- Mixing grams and kilograms. Both mass fields expect grams.
Related tools
The molarity calculator converts solution volumes into moles for reactions run in solution. The mass percent calculator and dilution calculator help prepare reagents, and the reaction rate calculator deals with how fast the yield is reached rather than how much.
External references
Frequently asked questions
What is the difference between theoretical and actual yield?
Theoretical yield is the calculated maximum from stoichiometry. Actual yield is what you weigh after isolating and drying the product.
Can the theoretical yield be in moles instead of grams?
The calculator shows moles of product as an intermediate result; use that figure if moles are required.
What ratio do I enter if two moles of reactant give one mole of product?
0.5. The ratio is always product coefficient over reactant coefficient.
Does the calculator find the limiting reactant?
No. Determine it first by comparing moles divided by coefficients, then enter that reactant’s data.
Why is my actual yield higher than the theoretical yield?
The product is not pure or not dry, or the wrong limiting reactant was used. Dry the sample and recheck the stoichiometry.