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The change in internal energy for a system going from state A to state B is 40 kJ/mol. If the system reaches B from A through a reversible process and then comes back to A through an irreversible process, what is the overall change in internal energy for the complete cycle?

1. Greater than 40 kJ
2. Less than 40 kJ
3. Zero
4. 40 kJ

Correct answer: Zero

Solution

The overall change in internal energy for a complete cycle is always zero, regardless of the path taken, because internal energy is a state function that depends only on the initial and final states.

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