Passage IV

Ammonia (NH₃) can be produced according to the chemical equation

N₂ + 3H₂2NH3

The equilibrium arrow () indicates that this reaction proceeds in both directions until it is at equilibrium, so that both the forward reaction (production of NH₃ ) and the backward reaction (production of N₂ and H₂ ) occur at the same rate. Equilibrium can be shifted forward or backward by changing the temperature, pressure, or concentration of reactants or products.

Two experiments were done using the following apparatus to produce NH₃.

In each trial, Steps 1−4 occurred:

1. A fresh catalyst (Catalyst W, X, Y, or Z), 160 kg of H₂, and 745 kg of N₂ were placed in the reactor.

2. The H₂ and N₂ reacted at a constant temperature and a constant pressure until equilibrium was established.

3. A mixture of NH₃ and any unreacted H₂ and N₂ flowed through Pipe A to a −50°C condenser at 1 atmosphere (atm) of pressure.

4. NH₃ condensed and exited the apparatus. (H₂ and N₂ do not condense at −50°C.) Any unreacted H₂ and N₂ flowed into Pipe B, returning to the reactor.

Steps 2−4 reoccurred in cycles until no more H₂ and N₂ returned from the condenser.

Experiment 1

A set of 9 trials was conducted with each of the 4 catalysts. For each set, the pressure was 150 atm; within each set, the temperature was different for each trial. Figure 1 shows, for each trial, the number of cycles of Steps 2−4.

Experiment 2

Four sets of 9 trials each were conducted with Catalyst Z. For each set, the temperature was different; within each set, the pressure was different for each trial. Figure 2 shows, for each trial, the amount of NH₃ produced in the first cycle of Steps 2−4.

Diagram and figures adapted from Jayant M. Modak, "Haber Process for Ammonia Synthesis." ©2002 by Indian Academy of Sciences.