13 past paper MCQs on Haber's Process, from the
Chemical Equilibrium unit of MDCAT Chemistry. The year each question appeared is shown
where known; tap “Show answer” for the correct option and a short solution.
1.Identify the CORRECT conditions required for the maximum yield of ammonia by Haber's process: (MDCAT 2024)
high pressure, low temperature and continual removal of ammonia
low pressure, low temperature and continual removal of ammonia
high pressure, high temperature and continual removal of ammonia
high pressure, low temperature and continual addition of ammonia
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Correct answer: (a) high pressure, low temperature and continual removal of ammonia
The forward reaction is exothermic and goes with a fall in the number of moles, so pressure helps, heat hurts, and taking the ammonia out keeps pulling it forward.
2.According to Le Chatelier's principle, in Haber's process yield of ammonia can be increased by: (SZABMU MDCAT 2025)
decreasing pressure and increasing temperature
increasing pressure and decreasing temperature
increasing volume and decreasing temperature
decreasing concentration of H2
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Correct answer: (b) increasing pressure and decreasing temperature
The forward reaction is exothermic and goes from four molecules to two, so high pressure and low temperature favour it.
3.Identify the CORRECT option required for the maximum yield of ammonia by Haber's process: (UHS MDCAT 2024)
High pressure low temperature continual removal of ammonia
Low pressure low temperature continual removal of ammonia
High pressure high temperature continual removal of ammonia
High pressure low temperature continual addition of ammonia
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Correct answer: (a) High pressure low temperature continual removal of ammonia
The forward reaction is exothermic and contracts in volume, and taking the ammonia away keeps pulling it forward.
4.Consider N2 + 3H2(g) ⇌ 2NH3(g) ΔH= -92.46kJ/mol The optimum temperature (°C), to produce ammonia is (KMU MDCAT 2024)
450
500
5000
Constant temperature
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Correct answer: (a) 450
About $450^{\circ}\mathrm{C}$ is the compromise between a good yield and a workable rate.
5.What conditions should be applied to minimize the leftover reactants in Ammonia synthesis? (NUMS MDCAT 2024)
200atm, 500°C
400atm, 200°C
100atm, 400°C
200atm, 400°C
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Correct answer: (d) 200atm, 400°C
High pressure drives the contraction forward, and $400^{\circ}\mathrm{C}$ is warm enough to reach equilibrium quickly.
6.For the chemical reaction: N2(g) + 3H2(g) ⇌ 2NH3(g) + Heat We can get maximize the yield of NH3: (SZABMU MDCAT 2023)
By increasing the temperature
By decreasing the pressure
By increasing the volume of the reaction vessel
By continuous withdrawal of ammonia after intervals
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Correct answer: (d) By continuous withdrawal of ammonia after intervals
Taking the ammonia away as it forms keeps drawing the equilibrium forward.
7.The high pressure of 200 atm in Haber’s process is used for: (SZABMU MDCAT 2023)
Better yield
Lower yield
Lower rate
Cost decrease
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Correct answer: (a) Better yield
The forward reaction contracts from four molecules to two, so pressure favours it.
8.Nitrogen and Hydrogen present in equilibrium mixture in Haber Process remain in (PMC MDCAT 2022)
Solid state
Liquid state
Gaseous state
Mixture of solid and gas
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Correct answer: (c) Gaseous state
The synthesis is run at about $450^{\circ}\mathrm{C}$, well above the boiling point of all three gases.