# Explain how the concepts of limiting reagent and percentage yield are used together to evaluate the efficiency of a chemical synthesis, using the reaction of ethanol with ethanoic acid to form ethyl ethanoate and water as your example.

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

> Ethanol and ethanoic acid react according to the equation: CH₃COOH(l) + C₂H₅OH(l) ⇌ CH₃COOC₂H₅(l) + H₂O(l). In a synthesis, 0.50 mol of ethanoic acid is mixed with 0.30 mol of ethanol in the presence of a small amount of concentrated sulfuric acid catalyst.

## Mark scheme (4 marks)

1. Ethanol is identified as the limiting reagent because it is present in the smaller molar amount (0.30 mol) relative to the 1:1 stoichiometric ratio required.
2. The theoretical yield of ethyl ethanoate is 0.30 mol, calculated from the amount of the limiting reagent (ethanol) and the 1:1 mole ratio in the equation.
3. Percentage yield is calculated as (actual yield / theoretical yield) × 100%, and a value below 100% indicates that not all of the limiting reagent was converted to product.
4. The reversible nature of the esterification equilibrium means the reaction does not go to completion, so the percentage yield will always be below 100% even without experimental losses; this illustrates a fundamental limitation on synthesis efficiency.

## Key terms

- [limiting reagent](https://www.gradenine.co.uk/glossary/limiting-reagent)
- [percentage yield](https://www.gradenine.co.uk/glossary/percentage-yield)

## Related

- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
- [How to answer "Explain" questions](https://www.gradenine.co.uk/tools/command-word-cheatsheet)
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Source: [GradeNine](https://www.gradenine.co.uk/q/explain-how-the-concepts-of-limiting-e414bbd7) · Published by Druglandscape Ltd.