What is percent atom economy?

Percent atom economy (PAE) is a green chemistry metric that expresses the fraction of atoms from all reactants that are incorporated into the desired product. It was introduced by Barry Trost in 1991 and is calculated as: PAE = (MW of desired product × stoichiometric coefficient) / (sum of MW × stoichiometric coefficient for all reactants) × 100.

What does a 100% atom economy mean?

A 100% atom economy means every atom from the reactants ends up in the desired product — no atoms are wasted as byproducts. Addition reactions (e.g., hydrogenation) often achieve this ideal.

How is atom economy different from percent yield?

Percent yield measures how much of the theoretical maximum product was actually obtained in an experiment. Atom economy is a theoretical property of the reaction equation itself, independent of how well the reaction runs. A reaction can have high atom economy but low yield, or vice versa.

Why is atom economy important in green chemistry?

High atom economy reduces waste, lowers raw material costs, and decreases the environmental burden of a chemical process. The 12 Principles of Green Chemistry list atom economy as principle #2, emphasizing its importance in sustainable synthesis design.

Where do I find the molar mass of a compound?

The molar mass equals the sum of atomic weights of all atoms in the molecular formula, in g/mol. For example, water (H₂O) = 2×1.008 + 15.999 ≈ 18.015 g/mol. Use a periodic table or a molecular weight calculator to find this value.

Percent Atom Economy

Calculate the percent atom economy of a reaction by entering the molar masses of reactants and desired product.

Reactants

Desired Product

Coeff.

Molar Mass (g/mol)

product

Enter reactant and product data, then click Calculate.

Quick Reference — Common Molar Masses

H₂O = 18.02 g/mol CO₂ = 44.01 g/mol HCl = 36.46 g/mol NaCl = 58.44 g/mol H₂SO₄ = 98.08 g/mol NaOH = 40.00 g/mol CH₃OH = 32.04 g/mol C₂H₅OH = 46.07 g/mol

Summary

Percent atom economy (PAE) is a key green chemistry metric developed by Barry Trost that measures how efficiently atoms in reactants are incorporated into the desired product. A value of 100% means every atom ends up in the target molecule, while lower values indicate wasted atoms that become byproducts or waste streams. PAE is calculated as (molar mass of desired product × its coefficient) ÷ (sum of molar masses of all reactants × their coefficients) × 100.

How it works

Enter the stoichiometric coefficient and molar mass (g/mol) for each reactant.
Add as many reactants as needed using the "Add Reactant" button.
Enter the stoichiometric coefficient and molar mass of the desired product.
Click "Calculate" to compute percent atom economy.
Review the result and the breakdown showing total reactant mass vs. desired product mass.

Use cases

Evaluate the green chemistry credentials of a proposed synthesis route.
Compare alternative reaction pathways for the same target molecule.
Teach green chemistry principles in undergraduate courses.
Screen reactions for industrial scale-up with minimal waste generation.
Calculate atom economy for multi-step synthesis sequences.
Assess catalytic vs. stoichiometric reagent choices.
Report sustainability metrics in process chemistry documentation.
Guide solvent and reagent selection in pharmaceutical manufacturing.

Frequently Asked Questions

Last updated: 2026-09-30 · Reviewed by Nham Vu