Theoretical Yield Calculator
Calculate theoretical yield, percent yield, and analyze chemical reaction efficiency.
Calculation Type
Reactant Information
Results
Theoretical Yield
Percent Yield
Mass Efficiency
How it works
Theoretical yield is the maximum product a chemical reaction can make from a given amount of reactant, assuming everything reacts perfectly. You convert the limiting reactant to moles, apply the reaction's mole ratio, then convert to product mass.
Theoretical yield
moles reactant → (mole ratio) → moles product → × molar mass = grams product
- limiting reactant
- the one that runs out first
- mole ratio
- from the balanced equation
Worked example
- 2 mol H₂ reacting with excess O₂
- 2H₂ + O₂ → 2H₂O
- Ratio H₂:H₂O = 2:2 = 1:1 → 2 mol water
- 2 mol × 18 g/mol
Theoretical yield = 36 g of water.
Good to know
- Identify the limiting reactant first — it caps how much product can form.
- Percent yield = (actual ÷ theoretical) × 100; it's always ≤ 100% in practice.
- Balance the equation before reading off the mole ratio.
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Frequently Asked Questions
What is theoretical yield?
It's the maximum amount of product a reaction could form if everything went perfectly, calculated from the limiting reactant via stoichiometry. Real experiments produce less, which is why chemists compare actual yield against it.
How do I calculate theoretical yield?
Balance the equation, convert the limiting reactant's mass to moles, use the mole ratio from the balanced equation to find moles of product, then multiply by the product's molar mass to get grams.
How do I identify the limiting reactant?
Divide each reactant's moles by its coefficient in the balanced equation; the smallest result is the limiting reactant. It runs out first and caps how much product can form — the other reactants are in excess.
What is percent yield?
Percent yield = (actual yield / theoretical yield) x 100. It measures reaction efficiency: incomplete reactions, side products, and losses during filtering or transfer all push it below 100%.
Can percent yield ever be over 100%?
Not legitimately — a result above 100% signals an error, most often product still wet with solvent, contamination with impurities, or a weighing mistake. Drying the product fully and re-weighing usually resolves it.