Thermodynamics of Electrolyte Solutions

For the calculation of the chemical potentials of the particular components in an electrolyte solution, it is necessary to define an appropriate standard and reference state. It is convenient to define a standard state where the values of both the concentration and the activity coefficient and hence the activity are unity. For the solvent, there is no problem to use the pure component at the required pressure and temperature as standard state as shown in Chapter 4  

For an electrolyte component, this standard state does not make sense, since the properties of electrolyte components such as HCl or NaCl in the pure state are totally different from the properties of an electrolyte solution. Instead, it is useful to define a hypothetical ideal solution at unit concentration as standard state  

Analogously, the mole fraction can be used as the concentration measure, again with the asymmetric convention for the activity coefficient  

A relationship between the standard chemical potentials formulated for mole fractions and molalities, respectively, can be derived from 

The relationship between the activity coefficients for the different concentration scales follows immediately from combining Eqs. (7.6), (7.14), and (7.16)  

---

Card D N and Valleau J 1970 Monte Carlo study of the thermodynamics of electrolyte solutions J. Chem. Phys. 52 6232... 

Andrew Dickson (Chair) is an Associate Professor-in-Residence at the Scripps Institution of Oceanography. His research focuses on the analytical chemistry of carbon dioxide in sea water, biogeochemical cycles in the upper ocean, marine inorganic chemistry, and the thermodynamics of electrolyte solutions at high temperatures and pressures. His expertise lies in the quality control of oceanic carbon dioxide measurements and in the development of underway instrumentation for the study of upper ocean biogeochemistry. Dr. Dickson served on the NRC Committee on Oceanic Carbon. He is presently a member of the IOC C02 Advisory Panel and of the PICES Working Group 13 on C02 in the North Pacific. 

These considerations can make the thermodynamics of electrolyte solutions tricky. Despite such possibilities, the right side of Eq. (3.18), p. 40, is typically inoffensive for the problems of ionic contributions to single-ion activities. In... 

Lee LL (2008) Molecular thermodynamics of electrolyte solutions. World Scientific Publishing, Singapore... 

Properties of ntmaqueous electrolyte solutions have been widely studied in fundamental research due to the possibility to vary parameters such as the viscosity and dielectric permittivity of the solvent. The result of these studies mainly conducted in the last century was a better knowledge of spectroscopic and transport properties as well as the thermodynamics of electrolyte solutions [3-17]. The observed behavior was interpreted in terms of stracture formation in solutions including solvation of ions, ion pair formation, formation of triple ions and clusters caused by the underlying interactions, the ion/ solvent molecule interaction and the ion/ion interaction [2, 5, 6, 9,14,18-21]. 

D. N. Card and J. P. Valleau, J. Chem. Phys., 52, 6232 (1970). Monte Carlo Study of the Thermodynamics of Electrolyte Solutions. 

---