ATOM ECONOMY measures how efficiently atoms from reactants are converted into the desired product — how much of the mass of reactants ends up in the useful product vs waste products.
EQUATION:
Atom economy (%) = (sum of relative formula masses of desired products ÷ sum of relative formula masses of ALL products) × 100
Note: this uses ALL products from the reaction (including waste), not just the desired one.
ALTERNATIVELY:
Atom economy (%) = (Mr of desired product ÷ sum of Mr of all products) × 100
A HIGH atom economy means:
Most reactant atoms end up in the desired product — efficient.
Little waste is produced.
A LOW atom economy means:
Many reactant atoms end up in waste products — inefficient.
More waste to dispose of — environmental and cost concerns.
Calculating Atom Economy
EXAMPLE 1 — high atom economy:
Manufacture of iron from iron(III) oxide:
Fe₂O₃ + 3CO → 2Fe + 3CO₂
Desired product: Fe (Mr = 56). Two atoms of Fe = 112.
All products: 2Fe (112) + 3CO₂ (3 × 44 = 132) → total = 244.
Atom economy = (112 ÷ 244) × 100 = 45.9%
EXAMPLE 2 — maximum atom economy (addition reactions):
Addition polymerisation: nCH₂=CH₂ → (—CH₂—CH₂—)ₙ
ONLY ONE PRODUCT formed — all atoms go into the polymer.
Atom economy = 100%
Reason: addition reactions always have 100% atom economy because ALL reactant atoms form the single product with no by-products.
EXAMPLE 3 — low atom economy:
Production of calcium oxide: CaCO₃ → CaO + CO₂
Mr of CaO = 56. Mr of CO₂ = 44. Total = 100.
Atom economy = (56 ÷ 100) × 100 = 56%
(44% of the mass becomes CO₂ waste)
Why Atom Economy Matters
GREEN CHEMISTRY and SUSTAINABILITY:
High atom economy = less waste = more sustainable process.
Green chemistry aims to design reactions with high atom economy.
ECONOMIC BENEFITS:
Fewer raw materials wasted → lower costs.
Less waste to dispose of → lower disposal costs.
ENVIRONMENTAL BENEFITS:
Less waste produced → fewer by-products to release or treat.
More sustainable use of raw materials.
COMPARING ROUTES:
Chemists choose synthetic routes with higher atom economy when possible.
Two routes to the same product may have very different atom economies.
ATOM ECONOMY vs PERCENTAGE YIELD:
These are different measures:
Atom economy: a property of the EQUATION — how efficient the chemistry is.
Percentage yield: a property of how the EXPERIMENT is carried out — how much is actually obtained.
Both should be maximised for efficient, sustainable chemistry.
ADDITION vs SUBSTITUTION reactions:
Addition reactions (one product only): atom economy = 100%.
Substitution/elimination reactions (multiple products): lower atom economy.
⚠️ Common Mistake
Atom economy uses the relative formula masses of the PRODUCTS (from the equation) — not the reactants. Divide the Mr of the DESIRED product by the sum of Mr of ALL products. Do not confuse with percentage yield — atom economy is about the equation; percentage yield is about the actual experiment.
📐 Key Equations
Atom economy (%) = (Mr of desired products ÷ sum of Mr of ALL products) × 100
📌 Key Note
Atom economy = (Mr desired product ÷ sum Mr all products) × 100. High atom economy = less waste = sustainable. Addition reactions: 100% atom economy (one product). Low atom economy = more waste by-products. Distinct from % yield — atom economy is a property of the reaction equation.
🎯 Matching Activity — Atom Economy
Match each scenario to atom economy or a related concept. — drag the symbols on the right to match the component names on the left.
100% atom economy
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Lower atom economy
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Why high atom economy matters
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Atom economy vs % yield
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Less waste, lower disposal costs, more sustainable use of raw materials
Decomposition of CaCO₃ → CaO + CO₂ — 44% of mass becomes CO₂ waste
Atom economy: efficiency of the equation. % yield: how much product is actually collected.
Addition polymerisation — only one product formed, all atoms go into the polymer
⚽ FIFA Worked Examples
Atom Economy Calculation
Calculate the atom economy for making ethanol (C₂H₅OH, Mr = 46) from the reaction: C₂H₄ + H₂O → C₂H₅OH
F
Atom economy = (Mr desired product ÷ sum Mr all products) × 100
I
Only one product: C₂H₅OH, Mr = 46. Sum of all products = 46
F
Atom economy = (46 ÷ 46) × 100
A
Atom economy = 100% — addition reaction, one product only
⭐ Higher Tier Only
Calculate atom economy using Mr values. Compare atom economy of different synthetic routes to the same product. Evaluate the economic and environmental importance of high atom economy in industrial chemistry. Explain why pharmaceutical manufacturers are encouraged to use reactions with high atom economy.
🔬 Triple Science Only
Atom economy (4.3.3.2) is chemistry-only — not in Combined Science. Students must calculate atom economy and explain its importance for sustainable and economically efficient chemistry.
🎯 Test Yourself
Question 1 of 2
1. A reaction produces 80 g of desired product and 20 g of waste product. What is the atom economy?
2. Why do addition reactions always have an atom economy of 100%?
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