Atom Economy
Practise Atom Economy for GCSE Chemistry with this free worksheet and full mark scheme — Foundation and Higher exam-style questions with worked answers for AQA, Edexcel and OCR. Atom economy = (Mr of the desired product ÷ total Mr of the reactants) × 100 — a higher value means a more sustainable process.
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These worksheets and mark schemes are original, written for Virtus Academy and checked against the current AQA, Edexcel and OCR specifications. Every worksheet comes with a full mark scheme.
Topic overview
Atom economy measures how much of the mass of the reactants ends up as the useful product. It is a measure of efficiency in terms of raw materials.
The formula is atom economy = (Mr of desired product ÷ total Mr of all reactants) × 100. Note that it uses relative formula masses from the balanced equation, not experimental masses.
A high atom economy is important for sustainable development and for economic reasons, because less waste is produced and fewer raw materials are used. A reaction with only one product has an atom economy of 100 per cent, which is why such reactions are preferred industrially.
Revision notes
The calculation
Atom economy = (Mr of desired product ÷ sum of Mr of all reactants) × 100.
Multiply each Mr by its balancing number from the equation. Use relative formula masses, not experimental masses — this is what distinguishes atom economy from percentage yield.
Why it matters
A high atom economy means less waste is produced and fewer raw materials are used.
This is important for sustainable development, and economically because waste must be disposed of and raw materials must be bought.
Atom economy versus percentage yield
Percentage yield measures how much of the possible product was actually obtained in practice.
Atom economy measures how much of the reactant mass could ever become useful product, even in a perfect reaction. A reaction can have a high yield but a poor atom economy if it produces a lot of by-product.
Key points
- Atom economy measures useful product as a proportion of reactants.
- Atom economy = (Mr of product ÷ total Mr of reactants) × 100.
- It uses relative formula masses, not experimental masses.
- A reaction with one product has 100 per cent atom economy.
- High atom economy means less waste.
- It differs from percentage yield.
Worked examples
Example 1
A reaction produces a desired product with Mr 56 from reactants with a total Mr of 100. Calculate the atom economy. [2 marks]
Model answer
Atom economy = (56 ÷ 100) × 100 (1 mark) = 56 per cent (1 mark).
Example 2
Explain why a high atom economy is important. [2 marks]
Model answer
Less waste is produced, so there is less to dispose of (1 mark), and fewer raw materials are needed, which reduces cost and is better for sustainable development (1 mark).
Example 3
Explain the difference between atom economy and percentage yield. [2 marks]
Model answer
Percentage yield compares the mass of product actually obtained with the theoretical maximum (1 mark). Atom economy compares the mass of the desired product with the total mass of all reactants, showing how much could ever become useful product (1 mark).
Common mistakes
Using experimental masses instead of Mr values.
Atom economy uses relative formula masses from the balanced equation.
Confusing it with percentage yield.
Yield is about what was actually obtained; atom economy is about what could be.
Forgetting the balancing numbers.
Multiply each Mr by its balancing number before adding.
Including only one reactant.
The denominator is the total Mr of ALL reactants.
Exam tips
- Use Mr values from the balanced equation, not masses.
- Multiply each Mr by its balancing number.
- Give both an environmental and an economic reason for high atom economy.
- Be ready to contrast atom economy with percentage yield.
Key terms
- Atom economy
- The proportion of reactant mass becoming useful product.
- Desired product
- The product the reaction is carried out to obtain.
- By-product
- An additional product that is not wanted.
- Sustainable development
- Meeting present needs without harming the future.
Related topics
Written and reviewed against the current AQA, Edexcel and OCR specifications. Spotted an error? Let us know.