This question is about ammonia and nitric acid. In the Haber process ammonia is produced from nitrogen and hydrogen. Figure 1 represents the Haber process.

Pipe P links the condenser to the reactor. Why is the condenser linked to the reactor?

The Haber process (N₂(g) + 3H₂(g) ⇌ 2NH₃(g)) is a reversible reaction that reaches equilibrium. This means that in the mixture leaving the reactor, there is ammonia product as well as unreacted nitrogen and hydrogen. In the condenser, the mixture is cooled. Ammonia has a much higher boiling point (-33 °C) than nitrogen (-196 °C) and hydrogen (-253 °C). Therefore, the ammonia condenses into a liquid and can be removed. The unreacted nitrogen and hydrogen remain as gases. Pipe P recycles these expensive unreacted gases back into the reactor to be passed over the catalyst again. This increases the overall yield and improves the economic efficiency of the process.