- #1

vincebs

- 148

- 1

## Homework Statement

Consider a gas with adjustable volume V, and diathermal walls, embedded in a heat bath of constant temperature T, and fixed pressure P. The change in the entropy of the bath is given by:

delta S_bath = delta Q_bath/T = -deltaQ_gas/T = -1/T (delta E_gas + P deltaV_gas)

By considering the change in entropy of the combined system, establish that ¨the equilibrium of a gas at fixed T and P is characterized by the minimum of the Gibbs free energy G = E + PV - TS¨

## The Attempt at a Solution

I tried assuming that the gas was ideal and found that delta S_gas would be NR ln (V2/V1) but I don´t see how that helps. I also tried writing down from the equation of G, that dG = dE + PdV - TdS, and saw that ifyou substitute the thermodynamic identity, dE = TdS-PdV, dG will equal zero but I don't think this is valid here.

Any ideas?

Thanks,

Vince