Electrolyte solutions and the Debye-Hiickel theory

The distinction between drinking water and seawater is obvious. Electrolyte solutions, as the name suggests, involve neutral components that separate into electrically non-neutral units, ions. Ionic interactions are q q y r for a pair of ions with formal charges q i and q separated by a distance r. 

Typical ionic interactions are strong on a thermal energy scale. We can characterize the strength of these interactions by considering the distance between monovalent ions when their mutual interaction potential energy corresponds to the standard thermal energy T = 298 K) r = 561 A. Because these inter- 

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 

We will begin a more detailed discussion from the point of view of a gaussian model Eq. (4.12), p. 66. Because we will be interested in the lowest concentrations, we will neglect consideration of short-ranged interactions they are necessary to define our problem but wouldn t appear in our final result here. Also because we are interested in the lowest concentrations (so the typical ionic interactions aren t too strong) and temperatures not too low (/3 not too high), the fact that the terms of Eq. (4.12), p. 66, exhibit a formal ordering in powers of /3 is also motivational. Thus, 

The discussion surrounding Eq. (4.13), p. 66, suggested it was reasonable to drop the subseript quahfier on (... )j. in treating the longest-ranged interactions. Noting that in that case the middle term of Eq. (4.71) vanishes by elecfroneutrality of the bulk compositions, we then consider the simplification 

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