Oxidation-reduction equations relating equilibrium constant

One of the first questions one might ask about forming a metal complex is how strong is the metal ion to ligand binding In other words, what is the equilibrium constant for complex formation A consideration of thermodynamics allows us to quantify this aspect of complex formation and relate it to the electrode potential at which the complex reduces or oxidizes. This will not be the same as the electrode potential of the simple solvated metal ion and will depend on the relative values of the equilibrium constants for forming the oxidized and reduced forms of the complex. The basic thermodynamic equations which are needed here show the relationships between the standard free energy (AG ) of the reaction and the equilibrium constant (K), the heat of reaction, or standard enthalpy (A// ), the standard entropy (AS ) and the standard electrode potential (E for standard reduction of the complex (equations 5.1-5.3). 

The general equation relating the equilibrium constant for a reaction involving the transfer of n electrons and standard oxidation-reduction potentials is... 

Equation (3-13) shows that the equilibrium pH of the bicarbonate buffer system of plasma can be to some extent controlled by varying the partial pressure of carbon dioxide in the air to which the blood is exposed (i.e. in the lungs). Reduction in partial pressure results in carbon dioxide leaving the blood with a rise in the last term of Equation (3-13) provided that the bicarbonate concentration remains constant. The equilibrium pH of the buffer system and hence the pH of the blood consequently rise. Conversely an increase in partial pressure of carbon dioxide in the alveolar air will result in a fall in the pH of blood plasma. In practice the partial pressure of carbon dioxide in the alveolar air is controlled by the rate of pulmonary ventilation in relation to the rate of production of carbon dioxide by metabolic oxidation within the body. Increased ventilation (i.e. hyperventilation) will lower the partial pressure of carbon dioxide and raise the blood pH, while decreased ventilation raises the partial pressure, making the blood more acid (metabolic acidosis). Normally the respiratory centre controls the rate of ventilation to keep the partial pressure of carbon dioxide close to the normal value of 40 mmHg. 

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