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2.1.5—Atom economy

Syllabus
First assessment 2025
Objective
2.1.5
Level
HL

Atom Economy

atomeconomy=(Mrofdesiredproduct/totalMrofreactants)×100%atom economy = (Mr of desired product / total Mr of reactants) × 100\%

Atom economy measures how much of the reactant mass is represented by the desired product. Low atom economy means more reactant mass becomes by-products and waste.

Apply stoichiometric coefficients to every formula mass before forming the ratio. Atom economy is fixed by the chosen equation and desired product, whereas percentage yield measures experimental recovery; a reaction can have high atom economy but poor yield, or the reverse.

Worked atom-economy example: 4 CHX3OH+2 CO+OX2→2 (CHX3O)X2CO+2 HX2O\ce{4CH3OH + 2CO + O2 -> 2(CH3O)2CO + 2H2O}, with dimethyl carbonate as the desired product. Atom economy=2(90.09)4(32.05)+2(28.01)+32.00×100=83.33%\text{Atom economy}=\frac{2(90.09)}{4(32.05)+2(28.01)+32.00}\times100=83.33\%. Coefficients multiply every molar mass. The remaining 16.67%16.67\% of reactant mass becomes the water by-product for this equation; actual percentage yield is a separate experimental measure.

Calculating Atom Economy

Assessment in practice

Representative question

Question 1

[Maximum number: 2]

Calculate the atom economy for the synthesis of ethyl ethanoate by the reaction below. Use sections 1 and 7 of the data booklet.

2C2H6( g)+Cl2( g)+32O2( g)→C4H8O2(l)+2HCl(aq)+H2O(l)2 \mathrm{C}_{2} \mathrm{H}_{6}(\mathrm{~g})+\mathrm{Cl}_{2}(\mathrm{~g})+\frac{3}{2} \mathrm{O}_{2}(\mathrm{~g}) \rightarrow \mathrm{C}_{4} \mathrm{H}_{8} \mathrm{O}_{2}(\mathrm{l})+2 \mathrm{HCl}(\mathrm{aq})+\mathrm{H}_{2} \mathrm{O}(\mathrm{l})

Amount of Chemical Change Summary

Retrieve the route: balance the equation, convert through the coefficient mole ratio, identify the limiting reactant, calculate theoretical and percentage yield, then assess atom economy.

Check formula subscripts, state symbols, ratio direction, units, the smallest normalized reactant amount, the theoretical-yield denominator, and the total reactant mass used for atom economy.