Temperature and Pressure effects: Ammonia is produced commercially by synthesis

Question

Temperature and Pressure effects: Ammonia is produced commercially by synthesis according to the reaction: 1/2 N_2 + 3/2 H_2 Grave NH_3 Assuming ideal gas behavior and stoichiometric feed, estimate, from the following thermodynamic data, the maximum theoretical yield of ammonia that can be achieved in a single pass reactor with outlet conditions maintained at 723 K at 500 atm. at one atm. Comment on your answers and explain why the commercial process is operated at high pressure. For NH_3(g) Delta H^f_298 = - 10.96 kcal/mol Delta = - 3.903 kcaL/mol Heat capacities at constant pressure (cal/mol K) Cp N_2 = 7.0 (independent of T) Cp H_2 = 7.0 (independent of T) Cp NH_3 = 6.126 + 0.008 T (K)

Explanation / Answer

N2 (g) + 3H2 (g) <======> NH3 (g)

you need to shift equilibrium in forward direction to produce the maximum possible amount of ammonia.

temperature: According to Le Chatelier's Principle, this will be favoured if you lower the temperature because reaction is exothermic(delta H -Ve).

The lower the temperature you use, the rate becomes slower . A manufacturer is trying to produce as much ammonia as possible per day.so we need to increase rate of reaction.

pressure: there are 4 molecules on the left-hand side of the equation, but only 2 on the right.According to Le Chatelier's Principle, increasing the pressure the equilibrium will shift in that direction where lower number of molecule is present.so you need as high a pressure .

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