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For a closed system undergoing an irreversible process, which of the following statements is INCORRECT?

1. Q_sys + Q_surr = 0
2. W_sys + W_surr = 0
3. delta_U_sys + delta_U_surr = 0
4. delta_S_sys + delta_S_surr = 0

Correct answer: delta_S_sys + delta_S_surr = 0

Solution

In a closed system: heat exchanged with surroundings satisfies Q_sys = -Q_surr (energy conservation), so Q_sys + Q_surr = 0 is correct. Similarly work done on surroundings equals work done by system: W_sys + W_surr = 0. Internal energy change of universe is zero by the first law: delta_U_sys + delta_U_surr = 0. However, for an irreversible process, the total entropy of the universe (system + surroundings) INCREASES: delta_S_universe = delta_S_sys + delta_S_surr > 0, not equal to zero. So the statement delta_S_sys + delta_S_surr = 0 is incorrect.

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