In a certain reversible expansion, a system at 300. K absorbs exactly 6.00 × 10² J of heat. In the irreversible recompression to the original state of the system, twice as much work is done on the system as is performed on the surroundings in the expansion. What is the entropy change of the system in the recompression step?

Question

Quizplus · Accepted Answer

The entropy change of the system in the recompression step is -2.00 J/K. This is because the entropy change for a reversible process is given by ΔS = q_rev/T, where q_rev is the heat absorbed by the system and T is the temperature in Kelvin. Since the system absorbs 6.00 J of heat in the expansion at 300 K, the entropy change for that step is ΔS = 6.00 J / 300 K = 0.02 J/K. In the recompression step, the process is irreversible, but the entropy of the universe must remain constant for the complete cycle. Since twice as much work is done on the system as is performed by it, the net work done on the system does not affect the entropy directly; however, the reversal of the process implies that the entropy change for the system in the recompression step is the negative of that in the expansion step, hence -0.02 J/K or -2.00 J/K when expressed correctly.

In a Certain Reversible Expansion, a System at 300