Reaction in an ideal gas mixture

Let us look in detail at the source of the minimum in G for the case of a reaction occurring in an ideal gas mixture in a closed system at constant T and p. During this process the system has only one independent variable, which it is convenient to choose as the advancement The additivity rule (Eq. 9.2.25) for the Gibbs energy is 

At = 0, the amounts and partial pressures have their initial values and pi  

Converting partial pressures to mole fractions with pi = yip and pi,o = Tj,oP gives 

There are four terms on the right side of Eq. 11.7.19. The first term is the Gibbs energy change for the reaction of pure reactants to form pure products under standard-state conditions, the second is a mixing term, the third term is constant, and the last term is an adjustment of G from the standard pressure to the pressure of the gas mixture. Note that the first and last terms are proportional to the advancement and cannot be the cause of a minimum in the curve of the plot of G versus It is the mixing term RT T that 

Thermodynamics and Chemistry, second edition, version 3 2011 by Howard DeVfoe. Latest version mnr.cheiti.viitid.edu/thennobook 

---

An example is the partial molar enthalpy Hi of a constituent of an ideal gas mixture, an ideal condensed-phase mixture, or an ideal-dilute solution. In these ideal mixtures. Hi is independent of composition at constant T and p (Secs. 9.3.3, 9.4.3, and 9.4.7). When a reaction takes place at eonstant T and p in one of these mixtures, the molar differential reaction enthalpy H is eonstant during the proeess, H is a linear function of and Af// and Ai7m(rxn) are equal. Figure 11.6(a) illustrates this linear dependence for a reaction in an ideal gas mixture. 

---