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Atom economy calculations: formulas and examples

Quantitative chemistry • Yield and atom economy

Key concepts

What you'll likely be quizzed about

  • Atom economy represents the percentage of reactant mass that becomes the desired product.
  • It is calculated using the relative formula masses (Mr) and the balanced chemical equation to account for all atoms.
  • Higher atom economy signifies fewer unwanted by-products, reducing waste and enhancing resource efficiency.

Flashcards

Test your knowledge with interactive flashcards

Calculation example: chlorination of methane prompt

Click to reveal answer

For CH4 + Cl2 → CH3Cl + HCl, the atom economy for CH3Cl equals (Mr CH3Cl ÷ (Mr CH4 + Mr Cl2)) × 100 ≈ (50.5 ÷ 87) × 100 ≈ 58.0%.

Key notes

Important points to keep in mind

Use a balanced equation for accurate mass contributions.

Apply Mr values for reactants and the desired product, including coefficients.

Atom economy relies on theoretical masses, not experimental yield.

High atom economy minimizes waste but does not guarantee overall process sustainability.

In reactions with unavoidable by-products, atom economy typically falls below 100%.

For multiple desired products, sum their masses in the numerator.

Round final percentages appropriately, indicating significant figures used.

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