Winter 2016 Midterm Question 3&4 D

[Ryan McDonough 4E]

The question asked me to find the delta S gas (entropy change of the gas).
I assumed that delta S gas was referring to delta S total not delta S system. I had the right idea and put that delta S total was 0 Joules. I could've figured out that delta S system was -2 Joules had I known what delta S gas was referring to. In addition to that, I got part E right when I put that delta S surrounding was 2 Joules. For next time, how do I differentiate between delta S system and delta S total when I am told to solve for delta S gas.

[Richard_4E]

You would need to identify in other problems which is the system and the surroundings. In this case, the ideal gas is the system since work is being done on it by the surroundings. Delta S total (also known as delta S universe) is equal to the Delta S System + Delta S Surroundings. Since it asked for the delta s of the gas and the gas is the system, it's asking for delta s system in this case.