# Explain how an atom economy calculation differs from a percentage yield calculation, and outline why a reaction with a high percentage yield may still be considered wasteful from a green chemistry perspective.

> IB DP Chemistry Standard Level (2023 syllabus) — R2.1 How much? The amount of chemical change · Explain · 4 marks

## Mark scheme (4 marks)

1. Percentage yield compares the actual (experimental) amount of product obtained to the theoretical (maximum possible) amount.
2. Atom economy is calculated from the balanced equation alone and compares the molar mass of the desired product(s) to the total molar mass of all reactants.
3. A reaction can have a high percentage yield yet a low atom economy if significant molar mass is incorporated into by-products rather than the desired product.
4. Green chemistry favours high atom economy to minimise waste and by-products, reducing environmental impact and resource consumption.

## Key terms

- [atom economy](https://www.gradenine.co.uk/glossary/atom-economy)
- [percentage yield](https://www.gradenine.co.uk/glossary/percentage-yield)
- [green chemistry](https://www.gradenine.co.uk/glossary/green-chemistry)

## Related

- [Revision notes for IB DP Chemistry Standard Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
- [Practice this with AI marking (free)](https://www.gradenine.co.uk/start)

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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-an-atom-economy-calculation-314251e0) · Published by Druglandscape Ltd.