Calculating atom economy

You calculate atom economy from the balanced equation, using relative formula masses (Mr). Multiply each Mr by its balancing number, which is the large number in front of the formula.

Atom economy = (Mr of the desired product ÷ sum of the Mr of all the reactants) × 100. The answer is a percentage. Because it uses only the balanced equation, it does not depend on the mass of reactant used.

Example: heating calcium carbonate, CaCO₃ → CaO + CO₂. The desired product is CaO with Mr 56. The only reactant has Mr 100. Atom economy = 56 ÷ 100 × 100 = 56%.

Example: extracting iron, Fe₂O₃ + 3CO → 2Fe + 3CO₂. The Mr of Fe₂O₃ is 160 and the Mr of CO is 28, so the reactants add up to 160 + (3 × 28) = 244. The desired product is iron, 2 × 56 = 112. Atom economy = 112 ÷ 244 × 100 = 46% (to 2 significant figures).