# Ammonia is produced industrially by the Haber process: N₂(g) + 3H₂(g) → 2NH₃(g). In a particular run, nitrogen gas is identified as the limiting reagent. Explain what is meant by the term 'limiting reagent' and describe how identifying the limiting reagent allows the theoretical yield of ammonia to be calculated.

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

## Mark scheme (4 marks)

1. The limiting reagent is the reactant that is completely consumed first / is present in insufficient molar quantity relative to the stoichiometric ratio.
2. The amount (in moles) of the limiting reagent determines the maximum moles of product that can form, because once it is consumed the reaction cannot proceed further.
3. The stoichiometric mole ratio from the balanced equation is used: moles of NH₃ = moles of N₂ × 2 (from the 1:2 ratio of N₂ to NH₃).
4. The theoretical yield (in grams) is then obtained by multiplying the calculated moles of NH₃ by its molar mass (17.04 g mol⁻¹).

## Key terms

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

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- [Revision notes for IB DP Chemistry Higher Level (2023 syllabus)](https://www.gradenine.co.uk/learn)
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Source: [GradeNine](https://www.gradenine.co.uk/q/ammonia-is-produced-industrially-by-the-f44bb228) · Published by Druglandscape Ltd.