Question

Which of these systems do work?

Answer 1

only #2 does work on the surroundings, since it's the only system where the number of gas molecules increases. This pushes harder on the walls of their container, making the system expand to keep the pressure constant. The P*DV is the system doing work on the surroundings.

Answer 2

2nd does work on the surroundings and work is done on the system in 1st