Stoichiometry & gases · SL/HL
Atom economy
Calculate the share of reactant mass in the desired product.
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Use decimal dots in datasets. Single values also accept decimal commas and scientific notation such as 1.2e-3 or 1.2 × 10⁻³.
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Formula & example
The relationship
What the variables mean
| Symbol | Meaning |
|---|---|
| Balanced-equation coefficient. | |
| Molar mass. |
Worked example
- Reactant terms
- 1 60.05 1 32.04
- Desired product coefficient
- 1
- Desired product molar mass / g mol⁻¹
- 74.08
80.44304%
Follow the example steps
- Reactant contribution: 1 × 60.05 = 60.05 g per stoichiometric reaction
- Reactant contribution: 1 × 32.04 = 32.04 g per stoichiometric reaction
- Desired-product contribution = 1 × 74.08 = 74.08
- Atom economy = 74.08 / 92.09 × 100 = 80.44304%
Common mistakes
Atom economy comes from the balanced equation, not measured yield.
Incorrect approach
Desired product 20 g mol⁻¹, total reactants 50 g mol⁻¹: use experimental yield.
Correct approach
Atom economy = 100 × 20/50 = 40%
More checks before you submit
- Balance the equation first.
- Do not substitute experimental yield into atom economy.
Method notes
Atom economy is a theoretical stoichiometric measure. It is different from percentage yield, which compares actual and theoretical product obtained.