A gas in a cylinder undergoes the following two-step process:
Step 1: At constant pressure the gas expands, doing 300J of work on the surroundings while 150J of energy is simultaneously transferred into the gas by heating.
Step 2: With the piston locked in place, the gas is cooled at constant volume, and 100J of energy is removed from the gas by heating.
What is the net change in internal energy ΔUnet for the gas for the combined process, and did the system ultimately gain or lose energy?
(a) +350J; the system gained energy
(b) −250J; the system lost energy
(c) +50J; the system gained energy
(d) +250J; the system gained energy