Try:
Atom economy = 56.0 %
- Mass of desired product = 1 × 56.08 g/mol =
56.08 g - Total mass of reactants = 1 × 100.09 =
100.09 g - Atom economy = 56.08 ÷ 100.09 × 100 =
56.0 %
44.0 % of the reactant mass ends up in by-products, even at 100 % yield.
How it works
Atom economy = (coefficient × molar mass of the desired product) ÷ (sum of coefficient × molar mass of all reactants) × 100. Because mass is conserved, the rest of the reactant mass must end up in by-products.
Addition reactions — where two molecules join into one — have 100 % atom economy. Substitution and elimination reactions always produce a by-product, so their atom economy is lower. Atom economy is different from percent yield: a reaction can have a high yield but a poor atom economy, and vice versa.
Frequently asked questions
- How do I calculate atom economy?
- Divide the total mass of the desired product in the balanced equation by the total mass of all reactants, and multiply by 100.
- What is the atom economy of making lime from limestone?
- CaCO₃ → CaO + CO₂: 56.08 ÷ 100.09 × 100 = 56.0 %. The other 44 % of the mass leaves as carbon dioxide.
- Why does atom economy matter in industry?
- A higher atom economy means less waste to treat or dispose of, better use of raw materials and often lower costs — which is why it is one of the principles of green chemistry.
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