Mixing of ideal gas and liquid solutions

When two ideal gases are mixed at a constant pressure, provided that no chemical reaction occurs, there is a difference between the free energy of the gases before and after the mixing. Before mixing, there are nA moles of gas A at pressure P and nB moles of gas B, also at pressure P. The total Gibbs free energy is 

After mixing, the total pressure is still P, but there will be (nA + nB) molecules. The partial 

Then the free energy change due to the mixing process is 

Since lnX, is always negative, it follows that ASmix is always positive and gives a maximum point for X = 0.5. Then, by combining Equations (369) and (370), one obtains 

For an ideal solution, we use fl instead of fl1 , which was used for gases. When the mixing of non-electrolyte liquids is considered, the ideal system is defined as one whose thermodynamic mixing parameters obey the same equations (Equations (368)—(371)), similar to an ideal gas, and A//mix = 0 also. 

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