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During an isothermal expansion, a confined ideal gas does −150 J of work against its surroundings. This implies that:

1. 150 J heat has been removed from the gas
2. 300 J of heat has been added to the gas
3. no heat is transferred because the process is isothermal
4. 150 J of heat has been added to the gas

Correct answer: 150 J of heat has been added to the gas

Solution

In an isothermal process, the internal energy of an ideal gas remains constant. Therefore, the heat added to the system equals the work done by the gas. Since the gas does -150 J of work, 150 J of heat must have been added to the gas.

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