Thermodynamics under nonstandard

Free enthalpy, according to Equation (1.55), depends on temperature and pjp° ratio. The ratio of partial pressures of the component i in the solution and in its standard state is called thermodynamic concentration, or relative activity, and more often simply activity. Then free enthalpy and chemical potential of the component i under nonstandard conditions are calculated from ... 

In Section 19.5 we saw a special relationship between A G and equilibrium For a system at equilibrium, AG = 0. We have also seen how to use tabulated thermodynamic data to calculate values of the standard free-energy change, AG°. In this final section, we learn two more way s in which we can use free energy to analy ze chemical reactions using A G° to calculate A G under nonstandard conditions and relating the values of A G° and K for a reaction. 

One thought you may have about corrosion is that we cannot expect standard conditions in real world applications. What must we do to account for the differences that arise when standard conditions are not present This is a very important question with clear ties to thermodynamics. The equation that describes cell potentials under nonstandard conditions is called the Nemst equation ... 

In Eq. (434) the interfreial electrostatic potential appears explicitly. The pseudo-standard state model would thus appear to be consistent wifli the BPD mass action equations 428 and 429. However, Eq. (433) has been derived under some very peculiar circumstances. Specifically, the chemical potentials in Eqs (432) and (434) are all standard state chemical potentials while the electrostatic Eq (433) is for variable, nonstandard states. Hence, it would seem that the derivation of adsorption equations by the pseudo-standard state method either violates thermodynamic principles or defines some very peculiar standard states. 

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