Debye-Hiickel term

Here, ydh is a Debye-Hiickel term, and Z) y and Ejjk are second and third virial coefficients, defined for each pair and triplet of ions in solution. As before, the values of D,j vary with ionic strength, whereas the terms Eijk are constant at a given temperature. 

It is shown that the properties of fully ionized aqueous electrolyte systems can be represented by relatively simple equations over wide ranges of composition. There are only a few systems for which data are available over the full range to fused salt. A simple equation commonly used for nonelectrolytes fits the measured vapor pressure of water reasonably well and further refinements are clearly possible. Over the somewhat more limited composition range up to saturation of typical salts such as NaCl, the equations representing thermodynamic properties with a Debye-Hiickel term plus second and third virial coefficients are very successful and these coefficients are known for nearly 300 electrolytes at room temperature. These same equations effectively predict the properties of mixed electrolytes. A stringent test is offered by the calculation of the solubility relationships of the system Na-K-Mg-Ca-Cl-SO - O and the calculated results of Harvie and Weare show excellent agreement with experiment. 

The Debye-Hiickel term, which is the dominant term in the expression for the activity coefficients in dilute solution, accounts for electrostatic, nonspecific long-range interactions. At higher concentrations, short-range, nonelectrostatic interactions have to be taken into account. This is usually done by adding ionic strength dependent terms to the Debye-Hiickel expression. This method was first outlined by Bronsted [5,6], and elaborated... 

The term Baj in the denominator of the Debye-Hiickel term has been assigned a value of Baj = 1.5, as proposed by Scatchard [9] and accepted by Ciavatta [10]. This value has been found to minimize, for several species, the ionic strength dependence of (y, /j between / = 0.5m and 4i = 3.5 m. It should be mentioned that some authors have proposed different values for... 

The Electrolyte NRTL model " and the Extended UNIQUAC model" are examples of activity coefficient models derived by combining a Debye-Hiickel term with a local composition model. Equation of state models with electrostatic terms for... 

The first term on the right is a modified Debye-Hiickel term where... 

The constants A and B in the Debye-Hiickel term equ 0.5154 and 0.3294 respectively at 32 C. Values of a and b are listed in Table 4.3, which is tor dominantly NaCl-type waters. We will use Parkhurst s (1990) values in the calculation. 

Here, k is the electronic transmission coefficient (k = 1 for adiabatic electron transfer) and v x the nuclear frequency factor, whereas is the equilibrium constant for assembly of a precursor state and effectively includes any coulombic work and medium (Debye-Hiickel) terms [4, 5]. Following the approach taken by Stranks [7], the observed volume of activation AV for a simple, adiabatic, outer-sphere, bimolecular electron transfer reaction can be represented as... 

D is the Debye-Hiickel term in molal units and /, the ionic strength converted to molal units by using the conversion factors listed in [76BAE/MES] (p.439). The following list gives the details of this calculation. The resulting uncertainties in log, p are obtained based on the rules of error propagation as described in Section C.6.2. 

Figure A-39 Logarithm of stability constants of nickel bisulphide complexes in seawater (NaCl solutions) plus the Debye-Hiickel term for ionic strength correction plotted as a function of ionic strength, T= 298.15 K. The solid lines correspond to least squares fits of the SIT model to the experimental data, [96LUT/RIC], A [94ZHA/MIL].

The term, Ba, in the denominator of the Debye-Hiickel term, D, cf. Eq. (B.2), has been assigned in this review a value of 1.5 kg moE- at 25°C and 1 bar, cf. Section B.1.1. At temperatures and pressures other than the reference and standard state, the following possibilities exist ... 

D is the Debye-Hiickel term in molal units and the ionic strength converted to molal units by using the conversion factors listed in Table II-5. The following list... 

The Debye-Hiickel term A 4l ( + ), differs from the corresponding term... 

Figure 6. and related parameters for an aqueous solution of (NH )jSO calculated based on the work of Clegg et al. (1996). Debye-Hiickel term is the first two terms in Eq. (B2), and shortrange forces corresponds to the third and fourth terms in the same equation. 

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