A container of ideal gas at STP undergoes an isothermal expansion and its entropy changes by 3.7 J/K.How much work does it do? A) zero B) 1.0 $\times$ 10³ J/K C) -1.0 $\times$ 10³ J/K D) none of the above.

Question

Quizplus · Accepted Answer

Because the process is isothermal, the temperature remains constant and, therefore, ΔU = 0. From the first law of thermodynamics (ΔU = Q - W), it follows that Q = -W. Since the entropy change is positive (ΔS > 0), the heat cannot flow from a cold reservoir to a hot one. Therefore, the expansion is done by the system (it is not done on the system). Hence, W = -Q = -ΔU = 0. However, the answer choices do not include zero, but only numerical values, so the closest one is B.

A Container of Ideal Gas at STP Undergoes an Isothermal ×\times×

A Container of Ideal Gas at STP Undergoes an Isothermal $\times$