Gibbs free energy diagram

Figure 7.8 Gibbs-free-energy diagram showing a wider range of products accessible from the excited-state R than from the ground state...

Fig. 1. Gibbs free energy diagram for the ATP-induced dissociation of actomyosin...

Fig. 5. Gibbs free energy diagram to show the mutual destabilization of bound calcium and phosphate in E-P Ca2 through the interaction energy AGj [31]... 

Fig. 7. Gibbs free energy diagrams for the interaction of a receptor with an agonist and an antagonist at equilibrium...

FIGURE 3.9 Gibbs free energy diagram for ammonia synthesis on the stepped Ru(OOOl) surface at 1,10, and 100 har. The numbers correspond to the six different reaction steps (see also Figs. 2.6 and 3.9) as defined in the preceding text. Data was obtained from the CatApp and corrected for ZPE and entropy contrihutions. The entropy of adsorbed species was assumed to be zero. Reaction conditions are as follows T = 700 K, = 1 3, conversion to ammonia = 10%. 

Because the Gibbs free energy of reaction is negative, the formation of products is spontaneous (as indicated by the green region in the diagram) at this composition and temperature. 

To see how the catalyst accelerates the reaction, we need to look at the potential energy diagram in Fig. 1.2, which compares the non-catalytic and the catalytic reaction. For the non-catalytic reaction, the figure is simply the familiar way to visualize the Arrhenius equation the reaction proceeds when A and B collide with sufficient energy to overcome the activation barrier in Fig. 1.2. The change in Gibbs free energy between the reactants, A -r B, and the product P is AG. 

Based on the standard Gibbs free energy of the various oxides, three triple points can be calculated WO2.72. WO2.9, WO2 at about 600°C, W02,9, WO3, WO2 at about 270°C, and WO2, WO2.72, W at 1480°C. Using this data, a phase diagram can be constructed. The stability of the various oxides is shown in Fig. 8.2 with respect to the partial pressures of H2O and H2, and temperature. Because aU of these compositions are equilibrium compositions, any of them can be produced simply by annealing W or WO3 at the given partial pressure ratio and temperature. 

A recent study by Holdaway and Mukhopadhyay (1993) essentially confirms the stability diagram of Holdaway (1971). However, it is of interest to show how even slight errors in the assigned Gibbs free energy of a phase drastically affect the stability fields of polymorphs. 

Let us call the melt phase a and the solid phase with complete immiscibility of components y. P is constant and fluids are absent. The Gibbs free energy relationships at the various T for the two phases at equilibrium are those shown in figure 7.2, with T decreasing downward from Ty to Tg. The G-X relationships observed at the various T are then translated into a T-X stability diagram in the lower part of the figure. 

At Ty, the Gibbs free energy of phase a (i.e., melt) at all compositions is lower than that of mechanical mixture y + y" phase a is then stable over the whole compositional range. At T2, the chemical potential of component 1 in a is identical to the chemical potential of the same component in y . Moreover, the equahty condition is reached at the standard state condition of the pure component T2 is thus the temperature of incipient crystallization of y. At T, the Gibbs free energy of a intersects mechanical mixture y + y" on the component 1-rich side of the diagram and touches it at the condition of pure component 2. Applying the prin-... 

Figure 7,8 Gibbs free energy curves and T-X phase relations for an intermediate compound (C), totally immiscible with pure components. Column 1 Gibbs free energy relations leading to formation of two eutectic minima separated by a thermal barrier. Column 2 energy relations of a peritectic reaction (incongruent melting). To facilitate interpretation of phase stability fields, pure crystals of components 1 and 2 coexisting with crystals C are labeled y and y", respectively, in T-X diagrams same notation identifies mechanical mixtures 2-C and C-1 in G-X plots.

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