About the Atom Economy Calculator
This atom economy calculator measures how efficiently a balanced reaction turns reactant atoms into the product you actually want. Enter the molar mass and stoichiometric coefficient of the desired product and of up to four reactants, and it returns the percent atom economy, the mass of by-products formed per kilogram of product and the minimum (theoretical) E-factor.
Atom economy is one of the core metrics of green chemistry, introduced by Barry Trost in 1991. It is used in GCSE, A-level and university chemistry courses and by process chemists comparing synthetic routes: an addition reaction such as hydrating ethene to ethanol scores 100%, while substitution and elimination reactions always lose some atoms to by-products.
The figure is purely theoretical — it assumes the reaction goes to completion with stoichiometric amounts. It ignores yield, excess reagents, solvents and catalysts, so pair it with a percent yield calculation to judge a real process.
With the default inputs, the atom economy is 100%. Change any value above to recalculate instantly.
How to use the atom economy calculator
- 1Write and balance the chemical equation.
- 2Enter the molar mass and coefficient of the product you want.
- 3Enter the molar mass and coefficient of each reactant (leave unused rows at 0).
- 4Read the atom economy and the by-product mass per kilogram of product.
Formula and method
Atom economy compares the mass of the desired product with the total mass of all reactants in the balanced equation, each multiplied by its stoichiometric coefficient. Because mass is conserved, the difference is the mass of by-products, so 100% minus the atom economy is the share of atoms that are wasted even under perfect conditions.
The by-products per kilogram figure equals (100 ÷ AE − 1) and is the lowest E-factor (kg waste ÷ kg product) the route can ever achieve; real E-factors are higher once yield losses, solvents and work-up are included.
- M
- Molar mass in g/mol
- coefficient
- Number in front of each species in the balanced equation
- AE
- Atom economy, %
Worked examples
Ethene + water → ethanol
C₂H₄ (28.05) + H₂O (18.02) gives 46.07 g of reactants and 46.07 g of ethanol. All atoms end up in the product, so the atom economy is 100% — the hallmark of an addition reaction.
Blast furnace: Fe₂O₃ + 3CO → 2Fe + 3CO₂
Reactants total 159.69 + 3 × 28.01 = 243.72 g, of which 2 × 55.85 = 111.70 g is iron. Atom economy = 111.70 ÷ 243.72 × 100 = 45.8%; the remaining 132 g leaves as carbon dioxide.
Steam reforming for hydrogen: CH₄ + H₂O → CO + 3H₂
Only 3 × 2.016 = 6.048 g of the 34.06 g of reactants becomes hydrogen, an atom economy of 17.8%. Each kilogram of H₂ comes with about 4.6 kg of carbon monoxide unless that CO is used too.
Frequently asked questions
What is atom economy?+
Atom economy is the percentage of the total mass of reactants that ends up in the desired product, calculated from the balanced equation. It shows how much of the starting material is inevitably turned into by-products.
What is the difference between atom economy and percent yield?+
Percent yield compares the product you actually obtained with the theoretical maximum. Atom economy is fixed by the equation itself. A reaction can have a 95% yield and still a low atom economy if it produces heavy by-products.
Why is high atom economy important?+
Higher atom economy means less waste to treat or dispose of, better use of raw materials and usually lower cost. It is the second of the twelve principles of green chemistry.
Which reactions have 100% atom economy?+
Addition reactions (hydrogenation, hydration of alkenes), rearrangements and many cycloadditions such as the Diels–Alder reaction, because all reactant atoms are incorporated into a single product.
Should I include catalysts and solvents?+
No. Atom economy uses only the reactants and products in the balanced equation. Catalysts are not consumed and solvents are not part of the equation, though both count toward a full E-factor or process mass intensity.