I've been studying statistical mechanics for a while, the topic is very far from what I've learned till now so my questions may be superficial. When trying to see what my entropy is in an isobaric-isothermal ensemble, which turns out to be applicable in reactive systems, if I write my partition function $\Delta$ without the degeneracy factor $\Omega$, the answer I get from

$$S = \sum p_i\ln p_i$$


$$G = -T\ln\Delta$$

(with $T$ in energy units, $k_\mathrm{B} = 1$). However, if I take my systems to be in favor of a state or degenerate, I get

$$G + T\ln\Omega = -T\ln\Delta$$

Anywhere I read about this ensemble, the relationship for $G$ is in the first form and not the second, can someone give hints to some reading for what I'm missing here?


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