Oxidation-reduction reactions Gibbs energy changes

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... 

C. Electrode Potentials and Gibbs Energy Changes for Oxidation-Reduction Reactions... 

Since the reduction potential for the Fe(II) / Fe(III) couple is + 0.77 V at pH 7, the energy obtainable in this reaction is small. These bacteria always oxidize reduced sulfur compounds, too. Especially interesting is their oxidation of pyrite, ferrous sulfide (Eq. 18-24). The Gibbs energy change was calculated from published data325 using a value of Gf° for Fe (OH)3 of... 

Standard half-cell potentials can be used to compute standard cell potentials, standard Gibbs free energy changes, and equilibrium constants for oxidation-reduction reactions. 

The standard electrode potential E° of a redox reaction is a measure of the potential that would be developed if both reductants and oxidants were in their standard states at equal concentrations and with unit activities. The units of E° are volts and ° can be calculated from the Gibbs free energy change (AG ) of the redox reaction from the relationships... 

Figure 5.2.2 Plot of Gibbs free energy changes of the thermal reduction (green line) (Fe3(>4 = 3 FeO + 1/2 O2), FeO oxidation (red line) (3 FeO + CO2 = Fe3C>4 + CO), and overall reaction (blue line) (CO2 = CO + 1/2 O2) for the iron-oxide-based cycle. The vertical lines show the melting points of the indicated iron-oxide phases.

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