Gibbs Free Energy of Ideal Gas in Carnot Cycle

Question

Let's just say we have 2 moles of monoatomic (maybe helium) ideal gas that is doing a Carnot Cycle with reservoir temperature of 300 and 750 K.

Now, here's a simple question, what is the Gibb Free energy change from point A to point B and from point B to C in this process?

Because (do correct me if I'm wrong), I believe that we need to know the absolute value of the entropy in this case.

Chet Miller · Accepted Answer · 2022-08-16 11:18:52Z

1

Generally, along a reversible path, dG=-SdT+VdP. But, for the isothermal path between A and B, $$dG=VdP=nRT\frac{dP}{P}=-nRT\frac{dV}{V}$$

answered Aug 16, 2022 at 11:18

Chet Miller

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$\begingroup$ What about from B to C? $\endgroup$
– Hafiz Aji Aziz
Aug 16, 2022 at 11:46
$\begingroup$ That would involve the S at B (orC). $\endgroup$
– Chet Miller
Aug 16, 2022 at 15:43
$\begingroup$ Yes. But how do we calculate that? I mean, its not that we need $\Delta S$, rather we need S $\endgroup$
– Hafiz Aji Aziz
Aug 17, 2022 at 3:23
$\begingroup$ S is specified relative to some well-defined reference state. We don't need to know the absolute value of S in order to use it in practical calculations. $\endgroup$
– Chet Miller
Aug 17, 2022 at 10:55

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