Theoretical & Percentage Yield Calculator
Calculate theoretical yield from a balanced equation, percentage yield from actual results, and atom economy — core calculations in A-level and degree chemistry.
Yield Calculations Guide
Theoretical vs Actual Yield
Theoretical yield is the maximum possible product mass calculated from the stoichiometry of the balanced equation and the limiting reactant. Actual yield is what you actually isolate from the experiment. Percentage yield = (actual ÷ theoretical) × 100%. A 100% yield is theoretically possible but never achieved in practice. Typical yields: excellent lab technique 85-95%. Industrial processes 60-80% depending on conditions. Yields above 100% indicate a calculation error or impure product.
Why Yield Is Never 100%
Several factors reduce actual yield below theoretical: incomplete reactions — many reactions reach equilibrium before completion. Side reactions — other reactions consuming reactants. Purification losses — filtering, washing, and transferring product always loses some. Transfer losses — small amounts remain in vessels. Impure reactants — less active ingredient than assumed. Evaporation — volatile products lost during heating. In industrial chemistry, improving yield is a major economic driver —
Atom Economy
Atom economy = (molar mass of desired product ÷ total molar mass of all products) × 100%. High atom economy means less waste generated per unit of desired product. Example: making ethanol by fermentation (C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂): atom economy = (2 × 46) ÷ (2 × 46 + 2 × 44) × 100% = 92/180 × 100% = 51%. All the CO₂ is wasted. Addition reactions often have 100% atom economy — all atoms end up in the product. Substitution reactions typically have lower atom economy.
Green Chemistry Principles
Percentage yield and atom economy together measure the efficiency and sustainability of a reaction. Green chemistry aims to maximise both. A reaction with 95% yield but 20% atom economy wastes 80% of the reactant atoms in unwanted by-products. A reaction with 50% yield but 100% atom economy at least ensures that all atoms that do react end up in the useful product. Industrial chemists balance: yield (economic efficiency), atom economy (sustainability), selectivity (unwanted side products), and c
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