Q.Discuss the manufacture of Ammonia by Haber's process. OR Discuss the electronic configuration and oxidation states of Group 16 elements.
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Start your 14-day free trial to unlock the full solution →The Haber process manufactures ammonia by combining nitrogen and hydrogen over an iron catalyst under high pressure and moderate temperature, conditions chosen as a practical compromise between equilibrium yield and reaction rate.
Reaction: N₂(g) + 3H₂(g) ⇌ 2NH₃(g), ΔH ≈ −92.4 kJ/mol (exothermic, and the forward reaction reduces the number of gas moles from 4 to 2).
Conditions (chosen by Le Chatelier's principle):
- Pressure: since the forward reaction decreases the number of moles of gas, high pressure (~200 atm) favours the forward reaction and shifts the equilibrium towards more NH₃.
- Temperature: the forward reaction is exothermic, so low temperature would favour more NH₃ at equilibrium, but the rate would then be too slow. A moderate temperature (~723 K/450°C) is used as a compromise that gives a reasonable rate with an acceptable (though not maximal) equilibrium yield.
- Catalyst: finely divided iron, promoted with a small amount of molybdenum (or Mo/K₂O), speeds up the attainment of equilibrium without altering its position.
Process: a 1:3 mixture of N₂ and H₂ is compressed to about 200 atm and passed over the catalyst bed at 723 K. The exit gas mixture (containing NH₃ along with unreacted N₂/H₂) is cooled, which liquefies and separates out the ammonia; the unconverted N₂ and H₂ are recycled back into the converter to improve overall conversion efficiency.
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