Chemical reaction Gibbs energy diagram

Fig. 5-1. One-dimensional Gibbs energy diagram for reaction (5-1) in solution. Ordinate relative standard molar Gibbs energies of reactants, activated complex, and products Abscissa not defined, expresses only the sequence of reactants, activated complex, and products as they occur in the chemical reaction. AG° standard molar Gibbs energy of the reaction AG standard molar Gibbs energy of activation for the reaction from the left to the right.

Fig. 5-2. One-dimensional Gibbs energy diagram for a chemical reaction in three different solvents I, II, and III [cf. Fig. 5-1). (a) Reaction with non-solvated (solvent I) and solvated (solvent II) activated complex (preferential solvation of the activated complex) (b) Reaction with non-solvated (solvent I) and solvated (solvent III) reactants (preferential solvation of the reactants).

Fig. 5-3. One-dimensional Gibbs energy diagram for a chemical reaction in two different solvents I and II [cf. Figs. 5-1 and 5-2). AGj and AG, standard molar Gibbs energies of activation in solvents I and II AG jj and AGj jj standard molar Gibbs energies of transfer of the reactants R and the activated complex from solvent I to solvent II, respectively.

Figure 9-15 (A) Transition state diagram illustrating Gibbs energy vs reaction coordinate for conversion of reactants to products in a chemical reaction. (B) Contour map of Gibbs energy vs interatomic bond distances for reaction B + X - A —> B-X+A.

Thus if a mixture of chemical species is not in chemical equilibrium, any reaction that occurs must be irreversible and, if the system is maintained at constant T and P, the total Gibbs energy of the system must decrease. The significance of this for a single chemical reaction is seen in Fig. 15.1, which shows a schematic diagram of G vs. e, the reaction coordinate. Since e is the single variable that... 

Fig, 3-2. Variation of Gibbs free energy for the chemical reaction aA + bB cC + dD, Only reactants are present at the far left side of the diagram and only products at the far right side. 

The proposed approach leads directly to practical results such as the prediction—based upon the chemical potential—of whether or not a reaction runs spontaneously. Moreover, the chemical potential is key in dealing with physicochemical problems. Based upon this central concept, it is possible to explore many other fields. The dependence of the chemical potential upon temperature, pressure, and concentration is the gateway to the deduction of the mass action law, the calculation of equilibrium constants, solubilities, and many other data, the construction of phase diagrams, and so on. It is simple to expand the concept to colligative phenomena, diffusion processes, surface effects, electrochemical processes, etc. Furthermore, the same tools allow us to solve problems even at the atomic and molecular level, which are usually treated by quantum statistical methods. This approach allows us to eliminate many thermodynamic quantities that are traditionally used such as enthalpy H, Gibbs energy G, activity a, etc. The usage of these quantities is not excluded but superfluous in most cases. An optimized calculus results in short calculations, which are intuitively predictable and can be easily verified. 

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