Two ideal gases are in separate containers with the same initial temperature, density, and volumes. The container of gas 1 has a piston that is free to move up or down. Gas 2 is in a fixed-volume container. Both systems are placed into a reservoir of hot water and they come to equilibrium. Which statement about this situation is true?

1. Both the heat Q absorbed and the change in internal energy are the same for the two gases.
2. The heat absorbed is the same for the two gases but gas 1 has a larger change in internal energy.
3. The heat absorbed is the same for the two gases but gas 2 has a larger change in internal energy.
4. The changes in internal energy are the same for the two gases but gas 1 absorbs more heat.
5. The changes in internal energy are the same for the two gases but gas 2 absorbs more heat.

The right answer is 4: Both gases come to the same final (reservoir) temperature, so the changes in internal energy are the same. More heat is absorbed by gas 1, however, because the gas does work.