Excess Gibbs function

ACTIVITIES, EXCESS GIBBS FUNCTIONS, AND STANDARD STATES FOR NON ELECTROLYTES... 

DETERMINATION OF NONELECTROLYTE ACTIVITIES AND EXCESS GIBBS FUNCTIONS FROM EXPERIMENTAL DATA... 

Having established the definitions and conventions for the activity function and for the excess Gibbs function in Chapter 16, we are in a position to understand the experimental methods that have been used to determine numeric values of these quantities. 

EXCESS GIBBS FUNCTION FROM MEASUREMENT OF VAPOR PRESSURE... 

Although the description of deviations from ideality in terms of the excess Gibbs function gives us one quantity instead of the two activity coefficients of the two components of a binary solution, we still need to calculate the activity coefficients first, as observed in Equation (16.57). 

DETERMINATION OF NONELECTROLYTE ACRVITIES AND EXCESS GIBBS FUNCTIONS... 

In this chapter, we shall consider the methods by which values of partial molar quantities and excess molar quantities can be obtained from experimental data. Most of the methods are applicable to any thermodynamic property J, but special emphasis will be placed on the partial molar volume and the partial molar enthalpy, which are needed to determine the pressure and temperature coefficients of the chemical potential, and on the excess molar volume and the excess molar enthalpy, which are needed to determine the pressure and temperature coefficients of the excess Gibbs function. Furthermore, the volume is tangible and easy to visualize hence, it serves well in an initial exposition of partial molar quantities and excess molar quantities. 

Considerable information concerning structural effects on aqueous salt solutions has been provided by studies of the properties of mixed solutions (Anderson and Wood, 1973). In a mixed salt solution prepared by mixing YAm moles of a salt MX (molality m) with Yhm moles of a salt NX (molality m) to yield m moles of mixture in 1 kg of solvent, if W is the weight of solvent, the excess Gibbs function of mixing Am GE is given by (19) where GE is the excess function for... 

To compare the excess Gibbs function of mixtures of carbon tetrachloride and cyclohexane with a simple formula for regular mixtures. 

The partial vapour pressures of mixtures of carbon tetrachloride and cyclohexane were measured by Scatchard, Wood, and Mochel (J. Amer. Chem. Soc. 1939, 61, 3206). They applied corrections to convert vapour pressures to fugacities and derived values for the excess Gibbs function G- by means of the formula... 

This chapter deals with experimental methods for determining the thermodynamic excess functions of binary liquid mixtures of non-electrolytes. Most of it is concerned with techniques suitable for measurements in the temperature range 250 to 400 K and the pressure range 0 to 100 kPa. Techniques suitable for lower temperatures will be briefly reviewed. Techniques for measuring the molar excess Gibbs function G, the molar excess enthalpy and the molar excess volume will be discussed. The molar excess entropy can only be determined indirectly from either measurements of (7 and at a specific temperature = (If — C /T], or from the temperature dependence of G m [ S m = The molar excess functions have been defined by... 

The molar excess Gibbs function G T,p, x) of a liquid mixture of A -f B containing mole fraction jc of B in the liquid phase at temperature T and pressure is defined by ... 

The excess Gibbs function G and the total pressure p can be calculated from (x ,y) data by assuming G to have some functional form, for example ... 

The major application of this technique appears to be in determining the excess Gibbs function for mixtures of non-volatile liquids. 

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