Hydrochloric acid reacts with oxygen (O2) to form chlorine (Cl2) and water. Oxygen is fed in 25% excess, and it is fed as a stream of air rather than pure oxygen. The fractional conversion of HCl is 0.80.

1) Calculate the composition (mole fractions) of the product stream using the method of atomic species balances.

2) Calculate the composition (mole fractions) of the product stream using the method of molecular species balances.

3) In this case, the process was operated with air as the oxygen source. Alternatively, pure O2 can be separated from air and fed to the reactor. Sometimes one method is more cost effective and sometimes the other is. Explain the costs associated with each approach.