Gibbs energy molar reaction

A distinguishing aspect in electrode kinetics is that the heterogeneous rate constants, kred and kox, can be controlled externally by the difference between the inner potential in the metal electrode (V/>M) and in solution (7/>so1) that is, through the interfacial potential difference E = electrode setup (typically, a three-electrode arrangement and a potentiostat), the E-value can be varied in order to distort the electrochemical equilibrium and favor the electro-oxidation or electro-reduction reactions. Thus, the molar electrochemical Gibbs energy of reaction Scheme (l.IV), as derived from the electrochemical potentials of the reactant and product species, can be written as (see Eqs. 1.32 and 1.33 with n = 1)... 

Fig. 4-1. One-dimensional Gibbs energy diagram for an equilibrium reaction A B in the solvents 1 and 11. Ordinate standard molar Gibbs energies of the reactants A and B in solvents 1 and 11 Abscissa not defined. AG°(1) and AG°(11) standard molar Gibbs energies of reaction in solvents 1 and 11, respectively AGj°(A, 1 11) and AGj°(B, 1 11) standard molar Gibbs energies of transfer of the solutes A and B from solvent 1 to solvent 11, respectively [AGj°(A, 1 11) = G°(A in 1) - G°(A in 11), and AG°(B, 1 11) = G°(B in 1) - G°(B in 11)], cf. Eq. (2-12a) in Section 2.3 = transition state.

The (differential molar) Gibbs energy of reaction ArG of a transformation can be expressed analogously to how we dealt with the enthalpy of reaction Ar//. In the case of smaU conversions A, when p, T, f, f, . .. are again kept constant, we obtain ... 

This is the (differential molar) Gibbs energy of reaction already mentioned [cf. Eq. (24.22)]. 

The chemical potential in the standard state is identical with the molar Gibbs energy of formation Thus, the part on the left-hand side of Eq. (12.17) is id( ntical with the standard Gibbs energy of reaction Ag. The part... 

In reality, the enthalpy of reaction is strongly temperature-dependent. When the temperature dependence of the standard enthalpy of reaction with the help of the molar heat capacities is taken into account (see Eq. 12.6), the following values for the enthalpies of reaction, Gibbs energies of reaction, and equilibrium constants are obtained (see Example 12.8) ... 

Figure 9.1 Molar Gibbs energies when all products and reactants are pure compounds. The Gibbs energy of reaction is given by because all products and reactants are in their reference states, and this does not change during the reaction until one of the reactants disappears.

The first term on the right side of Eq. 11.8.2 is the standard molar reaction Gibbs energy, or standard molar Gibbs energy of reaction ... 

The standard molar Gibbs energy of reaction (8.12) on the mole fraction scale when dodecane is the diluent of the TBP is AG° = -46 kJ mol", the reaction being dominated by its enthalpy change, AH° = -55 kJ mof as determined by Marcus [30]. The net enthalpy change arises from the amount invested in desolvation (dehydration) of the uranyl ion (aq) and the two nitrate ions N03 (aq) but regained... 

For molar amounts, the standard Gibbs energy of reaction for the following reaction at 25°C is —457.14 kj ... 

For example, the standard reaction Gibbs energy for reaction A is the difference between the molar Gibbs energies of fructose-6-phosphate and glucose-6-phosphate in solution at 1 mol dm and 1 bar. 

TABLE III. Equilibria data for the proton-transfer reaction from p-rerr-butylcalix[4]arene and amines in benzonitrile at 298.15 K. Derived Gibbs energies (molar scale). 

Since the defects are very dilute and are not defined in the Lewis/RandaU limit, we choose a Henry s law reference state for them, i.e., /zn = Wzn and Jv = This state is the hypothetical pure species characterized by all a b interactions its properties are given by those at infinite dilution. Thus, we use the partial molar Gibbs energy at infinite dilution for these terms in the Gibbs energy of reaction. 

The thermodynamic function used as the criterion of spontaneity for a chemical reaction is the Gibbs free energy of reaction, AG (which is commonly referred to as the reaction free energy ). This quantity is defined as the difference in molar Gibbs free energies, Gm, of the products and the reactants ... 

The standard Gibbs free energy of reaction, AG°, is defined like the Gibbs free energy of reaction but in terms of the standard molar Gibbs energies of the reactants and products ... 

What Do We Need to Know Already The concepts of chemical equilibrium are related to those of physical equilibrium (Sections 8.1-8.3). Because chemical equilibrium depends on the thermodynamics of chemical reactions, we need to know about the Gibbs free energy of reaction (Section 7.13) and standard enthalpies of formation (Section 6.18). Ghemical equilibrium calculations require a thorough knowledge of molar concentration (Section G), reaction stoichiometry (Section L), and the gas laws (Ghapter 4). 

Equation 5 shows how the Gibbs free energy of reaction varies with the activities (the partial pressures of gases or molarities of solutes) of the reactants and products. The expression for Q has the same form as the expression for K, but the activities refer to any stage of the reaction. 

Gibbs free energy of reaction The difference in molar Gibbs free energies of the products and reactants, weighted by the stoichiometric coefficients in the chemical equation. 

The quantity a is the anodic transfer coefficient-, the factor l/F was introduced, because Fcf> is the electrostatic contribution to the molar Gibbs energy, and the sign was chosen such that a is positive - obviously an increase in the electrode potential makes the anodic reaction go faster, and decreases the corresponding energy of activation. Note that a is dimensionless. For the cathodic reaction ... 

There is a fundamental difference between electron-transfer reactions on metals and on semiconductors. On metals the variation of the electrode potential causes a corresponding change in the molar Gibbs energy of the reaction. Due to the comparatively low conductivity of semiconductors, the positions of the band edges at the semiconductor surface do not change with respect to the solution as the potential is varied. However, the relative position of the Fermi level in the semiconductor is changed, and so are the densities of electrons and holes on the metal surface. 

A particular component of a given phase can be characterized in terms of its content and ability to partake in various processes (chemical reactions, transport processes) using the partial molar Gibbs energy. For an electrically-charged phase, this quantity is termed the electrochemical potential of the ith component... 

Practically in every general chemistry textbook, one can find a table presenting the Standard (Reduction) Potentials in aqueous solution at 25 °C, sometimes in two parts, indicating the reaction condition acidic solution and basic solution. In most cases, there is another table titled Standard Chemical Thermodynamic Properties (or Selected Thermodynamic Values). The former table is referred to in a chapter devoted to Electrochemistry (or Oxidation - Reduction Reactions), while a reference to the latter one can be found in a chapter dealing with Chemical Thermodynamics (or Chemical Equilibria). It is seldom indicated that the two types of tables contain redundant information since the standard potential values of a cell reaction ( n) can be calculated from the standard molar free (Gibbs) energy change (AG" for the same reaction with a simple relationship... 

The extent of the reaction of carbon dioxide with water to form carbonic acid is fairly well known—less than 1%. However, for thermodynamic purposes we make no distinction between the two nonionized species, C02 and H2C03. We are thus concerned with the sum of the concentration of these species, a quantity that can be determined experimentally. We must therefore develop the methods used to define the standard state of the combined nonionized species and the standard molar Gibbs energies of formation. 

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