Equilibrium constant Gibbs energy and

This is a very important method for calculating equilibrium constants and Gibbs-energy changes. Its extension to the calculation of AT/ and AS values is considered on p. 360. 

Equilibrium constants and Gibbs energies of the reactions in microphases can be expressed also in terms of local distribution coefficients of the reagents and products. For the reaction (13) ... 

Equilibrium constants and Gibbs energies of complexation are given in Table 2.3. These data can be used to study the existence of a linear relation between AH° and AG° for the complexation of SbCls. A plot of AH° versus AG° values for 28 Lewis bases (mostly carbonyl compounds) is shown in Figure 2.2. Only 84% of the variance of AH° is explained by AG°. The lack of a linear AH—AG relationship has been attributed to pronounced... 

The Gibbs free energy of formation values. Figs. 10.9 and 10.10, can be used to estimate the dissociation pressure or the gas composition where surface scale formation will be thermodynamically feasible. Assuming the formation of the corrosion product follows a similar reaction as the decomposition of palladium-sulfide (Eq. 10.10), the correlation between the equilibrium constant and Gibbs free energy of formation is illustrated by Eq. 10.11. 

CALCULATING EQUILIBRIUM CONSTANTS FROM GIBBS ENERGY TABLES AND THEN USING EQUILIBRIUM CONSTANTS TO CALCULATE EQUILIBRIUM CONCENTRATIONS... 

Concept of Equilibrium Equilibrium Constants and Gibbs Free Energy... 

AGr Gibbs free-cnergy change The energy difference between reactants and products. When AG° is negative, the reaction is exergonic, has a favorable equilibrium constant, and can occur spontaneously. When AGC is positive, the reaction is endergonic, has an unfavorable equilibrium constant, and cannot occur spontaneously. 

The effect of temperature on the equilibrium composition arises from the dependence of the equilibrium constant on the temperature. The relation between the equilibrium constant and the standard Gibbs free energy of reaction in Eq. 8 applies to any temperature. Therefore, we ought to be able to use it to relate the equilibrium constant at one temperature to its value at another temperature. 

If two reactions differ in maximum work by a certain amount 8wm (= -SAG ), it follows from the Brpnsted relation [when taking into account the Arrhenius equation and the known relation between the equilibrium constant and the Gibbs standard free energy of reaction, A m = exp(-AGm/J r)] that their activation energies will differ by a fraction of this work, with the opposite sign ... 

Heat effects accompanying chemical reaction influence equilibrium constants and compositions as well as rates of reaction. The enthalpy change of reaction, AHr, is the difference between the enthalpies of formation of the participants. It is positive for endothermic reactions and negative for exothermic ones. This convention is the opposite of that for heats of reaction, so care should be exercised in applications of this quantity. Enthalpies of formation are empirical data, most often known at a standard temperature, frequently at 298 K. The Gibbs energies of formation, AGfl likewise are empirical data. 

TABLE 13.3 T-dependent Equilibrium Constant (KT), Gibbs Free Energy of Reaction (AGT), and Overall Entropic Shift (AAG = AG12oo — AG90o) for the Water Gas Shift Reaction (cf. Tables 13.1, 13.2, and Text), as Determined from Theoretically ( B3LYP ) or Empirically ( Hill ) Evaluated Statistical Thermodynamic Formulas Versus Experiment ( Exp. )... 

Calculate the equilibrium constant and the standard Gibbs energy change at 25°C for reaction 3 from the equilibrium constants obtained above for reactions 1 and 2. Show that AG° for reaction 3 = AG° of reaction 1 - AG° of reaction 2. 

One word about the Gibbs energies of adsorption. In equilibrium the molar Gibbs energy of adsorption is zero AadGm = /P — pT 0. The reason is simple. In equilibrium and for constant P and T the chemical potential of the molecules in the gas phase n9 is equal to the chemical potential of adsorbed molecules /P. What is not zero is the standard Gibbs energy of adsorption... 

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