Reduced standard-state chemical potential difference

In equations 27-29, P(j is the partial distribution coefficient of component ij, Tij is the ratio of activity coefficients, 0 is the reduced standard-state chemical potential difference, xiop is the standard-state chemical potential of component i in phase p, and yf and yxjp are the activity coefficients of components i and ij, respectively, in phase p. The working equations (equations 23-26) describing phase equilibria, along with the equation defining a mole fraction, are implicitly complex relations for T, P, x, y, xAC, xA, xc, and xD but involve only two thermodynamic quantities, 0 and Tiy Equations 23-25 are implicit in composition only through the term, which is itself only a weak function of composition. 

The thermodynamic quantity 0y is a reduced standard-state chemical potential difference and is a function only of T, P, and the choice of standard state. The principal temperature dependence of the liquidus and solidus surfaces is contained in 0 j. The term is the ratio of the deviation from ideal-solution behavior in the liquid phase to that in the solid phase. This term is consistent with the notion that only the difference between the values of the Gibbs energy for the solid and liquid phases determines which equilibrium phases are present. Expressions for the limits of the quaternary phase diagram are easily obtained (e.g., for a ternary AJB C system, y = 1 and xD = 0 for a pseudobinary section, y = 1, xD = 0, and xc = 1/2 and for a binary AC system, x = y = xAC = 1 and xB = xD = 0). 

Reduced Standard-State Chemical Potential Difference. The... 

Two types of variables appear in Equations 3 and 4, 0 and r The variable 0 is a reduced standard state chemical potential difference and is defined by... 

From a Solution Model. Calculation of the difference in reduced standard-state chemical potentials by methods I or III in the absence of experimental thermodynamic properties for the liquid phase necessitates the imposition of a solution model to represent the activity coefficients of the stoichiometric liquid. Method I is equivalent to the equation of Vieland (106) and has been used almost exclusively in the literature. The principal difference between methods I and III is in the evaluation of the activity coefficients... 

Four different methods were presented to determine the reduced standard state chemical potential change and applied to the Ga-Sb system. It is common practice to use Equation 7 and a solution model representing the stoichiometric liquid activities to determine 0. The solution model parameters are then estimated from a fit of the binary phase diagram. It has been shown that this procedure can lead to large errors in the value of 0. The use of Equation 9, however, gave the correct temperature dependence of 0 and the inclusion of activity measurements in the data base replicated the recommended values of 0Tp. 

In voltaic cells, it is possible to carry out the oxidation and reduction halfreactions in different places when suitable provision is made for transporting the electrons over a wire from one half-reaction to the other and to transport ions from each half-reaction to the other in order to preserve electrical neutrality. The chemical reaction produces an electric current in the process. Voltaic cells, also called galvanic cells, are introduced in Section 17.1. The tendency for oxidizing agents and reducing agents to react with each other is measured by their standard cell potentials, presented in Section 17.2. In Section 17.3, the Nernst equation is introduced to allow calculation of potentials of cells that are not in their standard states. 

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