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For a spontaneous process in an isolated system, which condition holds?

A $Δ S_{sys t e m} = 0$
B $Δ S_{sys t e m} < 0$
C $Δ U < 0$
D $Δ S_{sys t e m} > 0$

Answer: D

An isolated system exchanges no heat or work, so

Δ U = 0

and

Δ S_{s u rr} = 0

. The second law requires

Δ S_{t o t a l} > 0

for spontaneous change, hence

Δ S_{sys t e m} > 0

.

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