Atom Economy

Key Stage 4

Meaning

Atom Economy is the percentage of atoms in the reactants which ends up in the desired products.

About Atom Economy

During a chemical reaction there is often more than one product. When there is more than one product often one is desired and one is a waste product that must be disposed of.

To reduce costs and increase the efficiency of a process chemical engineers design systems that produce the maximum amount of a desired product and a minimum amount of waste products.

Atom Economy Equation

Percentage Atom Economy = [(Relative Formula Mass of Desired Product)/(Sum of Relative Formula Masses of Reactants)] x 100%

% Atom Economy = \(\frac{M_p}{M_r} \times 100%\)

Where:

M_p = Relative Formula Mass of Desired Product

M_r = Sum of Relative Formula Masses of Reactants

Example Calculations

Calculate the atom economy for producing Ammonia in the following reaction: N2(g) + 3H2(g) ⇌ 2NH3(g)	Calculate the atom economy for producing Calcium Oxide in the following reaction: CaCO3(s) → CaO(s) + CO2(g)	Calculate the atom economy for producing Sodium Chloride in the following reaction: HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l)
Find the Relative Formula Mass of the relevant reactants and product. Mr of N2 = 28g Mr of H2 = 2g Mr of NH3 = 17g	Find the Relative Formula Mass of the relevant reactants and product. Mr of CaCO3 = 100g Mr of CaO = 56g	Find the Relative Formula Mass of the relevant reactants and product. Mr of HCl = 36.5g Mr of NaOH = 40g Mr of NaCl = 58.5g
Find the total mass of reactants needed and the total mass of the desired product. Mass of Reactants = 28 + 3 x 2 Mass of Reactants = 34g Mass of desired Product = 2 x 17 Mass of desired Product = 34g	Find the total mass of reactants needed and the total mass of the desired product. Mass of Reactants = 100g Mass of desired Product = 56g	Find the total mass of reactants needed and the total mass of the desired product. Mass of Reactants = 36.5 + 40 Mass of Reactants = 76.5g Mass of desired Product = 58.5g
Substitute the values into the equation. % Atom Economy = \(\frac{M_p}{M_r} \times 100%\) % Atom Economy = \(\frac{34}{34} \times 100%\) % Atom Economy = 100%	Substitute the values into the equation. % Atom Economy = \(\frac{M_p}{M_r} \times 100%\) % Atom Economy = \(\frac{56}{100} \times 100%\) % Atom Economy = 56%	Substitute the values into the equation. % Atom Economy = \(\frac{M_p}{M_r} \times 100%\) % Atom Economy = \(\frac{58.5}{76.5} \times 100%\) % Atom Economy = 76.5%

References

AQA

Atom economy (atom utilisation), pages 79-80, GCSE Chemistry, Hodder, AQA

Atom economy, page 48, GCSE Chemistry; The Revision Guide, CGP, AQA

Atom economy, pages 138-140, GCSE Chemistry, CGP, AQA

Atom economy, pages 70-71, GCSE Chemistry; Third Edition, Oxford University Press, AQA