Gibbs free standard energy solution acidity

Now let us return to the approaches connected with the estimation of the primary medium effect for protons, log y0 n+, that are used for obtaining quantitative information on the acidity of pure protolytic or aprotic solvents relative to the standard solution of a strong acid in water. From the thermodynamics, these are known to be a measure of the Gibbs free energy of proton transfer from the standard solution in water to the one in a non-aqueous solvent (M). This parameter is connected with the energy of proton resolvation in the following way ... 

Since metallic zinc does actually dissolve in acid solutions, under conditions specified in the definition of a standard electrode, the standard change in Gibbs free energy must be negative for the first pair of reactions and positive for the second pair. The potential of the zinc couple, defined by AG° = —nFE° (n — number of electrons = 2, F = the Faraday), has to change sign accordingly. The half-reaction... 

Examples of excellent work in the literature, where the authors have taken care in their use of the best experimental value for the Gibbs free energy of solvation of the proton, and made careful use of thermodynamic cycles with attention to standard state issues, and made a good choice of methods for gas-phase and solution-phase calculations are listed here. These include the trimethylaminium ion [123], carboxylic acids [124],... 

Table 6.8 provides the Gibbs free energy of formation of different oxides and the corresponding standard potentials for aqueous solutions. Generally, the oxides of less noble metals exhibit a lower standard potential of formation. These metals passivate spontaneously in the presence of protons. Furthermore, many oxides exhibit good chemical stability in acidic environments. This explains the higher eorrosion resistance of metals such as titanium, tantalum and chromium. 

Calcium carbonate is insoluble in water. Yef it dissolves in an acidic solution. Calculate the standard enthalpy, entropy, and Gibbs free energy change for the reaction between sohd calcium carbonate and hydrochloric acid. What drives the reaction, the enthalpy change, or the entropy change ... 

AG° = change in Gibbs free energy of a reaction if negative, energy is released if positive, energy must be supplied AG = AG° for a reaction in solution under standard conditions but at a specified pH (here pH 7-0) lAA = indol-3yl-acetic acid IPP = isopentenyl pyrophosphate J = fluxes of ions Km = Michaelis constant... 

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... 

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