Electrochemical exchange

Relationships having the same form as eq 14 can also be written for the enthalpic and entropic contributions to the intrinsic free energy barriers (10). Provided that the reactions are adiabatic and the conventional collision model applies, eq 14 can be written in the familiar form relating the rate constants of electrochemical exchange and homogeneous self-exchange reactions (13) ... 

Rate Constants and Thermodynamic Parameters for Selected Electrochemical Exchange and Homogeneous Self-Exchange Reactions at 25°C. 

The sum of the exponents is close to unity. This equation now resembles eqn. (101) and so supports the idea of an electrochemical exchange mechanism at the platinum surface. However, quite different exponents (0.24 and 0.76, respectively) are predicted by electrode kinetic data [231]. As the concentration of Co(en)3+ rose further, the catalytic rate passed through a maximum because of the effect of competitive reactant adsorption. 

ELEX [ELectrochemical Exchange] A process for separating lithium isotopes for use in making lithium deuteride for use in nuclear weapons. Operated at Oak Ridge National Laboratory, TN, from 1951 to 1959, until this process was replaced by the COLEX process. 

The w,causes electrochemical exchange between the Mg and the Ag ion. The heat of reaction of this exchange provokes the pyrochemical effect. I a peroxide oxidizes Mg powd with incandescence (Ref 5). The mixt explodes when Heated to redness. When the mixt is exposed to moist air spontaneous combustion occurs., When carbon dioxide gas is passed over a mixt of powd Mg and Na peroxide, the mixt explodes (Ref 6). Stannic oxide, heated with Mg, explodes (Ref 13)., A mixt of sulfates and Mg may cause an expln (Ref 17.) It has been detd experimentally that a mixt of Mg powd with trichloroethylene or carbon tetrachloride will flash or spark under, Heavy impact (Ref 2l). Mg alloy powders contg more than 50% Mg readily ignite in air (Ref 20)... 

It is instructive to compare the energetics of such electrochemical exchange reactions ... 

Figure 2. Comparison between component potential-energy surfaces for elementary electrochemical exchange reaction for which the reaction entropy AS is positive (A) and resultant free-energy profile (B), plotted against the nuclear-reaction coordinate.

SCHEME 15.6 Electrochemical exchange between cisoid and transoid rotor confignrations of complexes 25 and 25", respectively. 

Part of the discrepancy between the calculated and experimental electrochemical oxidation rates of Fe(OH2)6 is due to electrostatic double-layer effects upon the apparent rate constants for electrochemical exchange. The standard rate constants measured at the formal potential for the redox couple concerned must be corrected for double-layer effects to obtain the corrected rate [45]. Such corrections depend on the electrode, electrolyte, Tafel coefficient, potential and charge of the redox couple. For the electrochemical exchange of the Fe(OH2)6 couple at the mercury/aqueous surface at 25 °C, the correction for the double-layer effects increase the rate from 2 x 10" to 1 x 10" cm sec" [38]. Thus, the disaepancy noted above is reduced to a factor of 200. 

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