A) The role of the heat exchanger is to pre-heat the incoming reactants (ammonia and air) using the heat from the hot product gases leaving the catalytic chamber. This conserves energy and ensures

Here are the answers to your questions based on the provided flowchart:

a) The role of the heat exchanger is to pre-heat the incoming reactants (ammonia and air) using the heat from the hot product gases leaving the catalytic chamber. This conserves energy and ensures the reactants reach the optimal temperature for the catalytic reaction.

b) In the catalytic chamber, ammonia is catalytically oxidized by oxygen (from the air) to form nitric oxide (NO) and water vapor. This is the first step of the Ostwald process for nitric acid production.
The reaction is: $$4NH_3(g) + 5O_2(g) \xrightarrow{catalyst} 4\text{