Question

Write suitable conditions of concentration, temperature, and pressure used during the manufacture of ammonia by Haber process.

Answer 1

1. Concentration: Addition of H₂ or N₂ both favours forward reaction. This increases the yield of NH₃.
2. Temperature: The formation of NH₃ is exothermic. Hence, low temperature should favour the formation of NH₃. However, at low temperatures, the rate of reaction is small. At high temperatures, the reaction occurs rapidly but the decomposition of NH₃ occurs. Hence, the optimum temperature of about 773 K is used.
3. Pressure: The forward reaction is favoured with high pressure as it proceeds with a decrease in the number of moles. At high pressure, the catalyst becomes inefficient. Therefore, optimum pressure needs to be used. The optimum pressure is about 250 atm.