Standard Gibbs energies of formation

Fig. 1. Standard Gibbs energy of formation vs temperature where changes in state are denoted as M, B, and S for melting, boiling, and sublimation points.

DELHF = Standard enthalpy of formation of vapour at 298 K, kJ/mol. DELGF = Standard Gibbs energy of formation of vapour at 298 K, kJ/mol. 

The relationships of the type (3.1.54) and (3.1.57) imply that the standard electrode potentials can be derived directly from the thermodynamic data (and vice versa). The values of the standard chemical potentials are identified with the values of the standard Gibbs energies of formation, tabulated, for example, by the US National Bureau of Standards. On the other hand, the experimental approach to the determination of standard electrode potentials is based on the cells of the type (3.1.41) whose EMFs are extrapolated to zero ionic strength. 

The terms EAgCl/AgjCi- and h+/h2 are designated as the electrode potentials. These are related to the standard electrode potentials and to the activities of the components of the system by the Nernst equations. By a convention for the standard Gibbs energies of formation, those related to the elements at standard conditions are equal to zero. According to a further convention, cf. Eq. (3.1.56),... 

The reaction isotherm of classical thermodynamics applied to the formation of the transition state relates K to AG0, the standard Gibbs energy of formation of the activated... 

The standard Gibbs energy of formation of NaCl is — 384 kJ mol 1 and that of NiCl2 is — 62kJmol 1. Calculate the ideal voltage of a ZEBRA cell. 

Figure 1.10 The standard Gibbs energy of formation from the binary constitutent oxides of the kyanite, sillimanite and andalusite modifications of A SiOs as a function of pressure at 800 K. Data are taken from [3]. All three oxides are treated as incompressible.

Solubility products can be derived indirectly from standard electrode potentials and other thermochemical data, and directly from tabulated standard Gibbs energies of formation, AfG°, of the ions in aqueous solution [12]. Thus, the use of... 

Figure 3.4. Ellingham diagram showing standard Gibbs energy of formation of various oxides as a function of temperature.

The thermodynamically stable form of bulk platinum in oxygen saturated water at ambient conditions is the completely hydrated platinum(IV)oxide, Pt02 4H20, also referred to as platinic acid H2Pt(OH) 14yl5) with a standard Gibbs energy of formation of -84 kJ mol" The formation of this compound will be even more favoured in the case of incompletely coordinated platinum. 

Table 2.2 contains the standard Gibbs energies of formation and the standard enthalpies of formation of a selection of anions at 298.15 K (25 °C). 

Table 2.3 contains the standard Gibbs energies of formation and the standard enthalpies of formation of a selection of main group cations at 25 °C. They refer to the formation of 1 mol dm- solutions of the cations from their elements and are relative to the values for the hydrated proton taken as zero. 

Table 7.4 Standard Gibbs energies of formation and standard enthalpies of formation of some transition element monatomic cations and that of Ga3+ at 298 K (in kJ mol 1) ...

The data required for method II are the measurable quantities AGf°[ij] and, if Kn is not 0, AHmn, Tmn, and Cps[n] and an extrapolated quantity Cp[n], To make use of available data, the standard Gibbs energy of formation can be expressed in terms of the standard enthalpy and entropy of formation. The advantage of this formulation is that thermodynamic information for unstable or metastable systems is required only for the elements (i.e., Cp[n]), for which a better estimate can usually be made. This data base contains no explicit liquid-solution properties. 

Klaning UK, Sehested K, Holcman J (1985) Standard Gibbs energy of formation of the hydroxyl radical in aqueous solution. Rate constants for reaction CI02 + O3 <=> 03 + CIO2. J Phys Chem 89 760-763... 

Mavrovouniotis, M.L. 1990. Group contributions for estimating standard Gibbs energies of formation of biochemical compounds in aqueous solution. Biotechnol. Bioeng. 36, 1070-1082. 

We consider only aqueous solutions here, but the methods used are applicable to any solvent system. The standard Gibbs energy of formation of a strong electrolyte dissolved in water is obtained according to Equation (11.28). In such solutions the ions are considered as the species and we are concerned with the thermodynamic functions of the ions rather than the component itself. We express the chemical potential of the electrolyte, considered to be MVtAv, in its standard state as... 

When the standard Gibbs energy of formation of the hydrogen ion is defined as zero, the standard molar Gibbs energy of hydronium ion must equal that of water. The change of state related to AGP(H30 + ) is... 

This equation permits the calculation of AG for any arbitrary condition when AGe is known from a study of the equilibrium condition or calculable from standard Gibbs energies of formation. 

The corresponding change in standard Gibbs energy is called the standard Gibbs energy of formation of C02, A/G298.i5, and is defined as... 

The first term on the right-hand side of this equation is the standard Gibbs energy of formation of methane, which is listed [2] as -50.460 kj/mol and thus EXch,cH4(g) can be calculated to be 831.6 kj/mol. Chapter 9 illustrates the use of this exergy value in the analysis of a natural gas-driven power station. 

Table 7.2 gives the standard chemical exergy of H20 and 02, respectively. Calculate with the help of Equation 7.13 the standard chemical exergy of H2. The standard Gibbs energy of formation for H20 can be found in [1],... 

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