The irreversible processes which occur in a binary electrolyte solution are described by a new formalism which uses observable variables. This is based on (i) the relationship of the electrochemical potential of ion constituents to the chemical potential of the electrolyte; (ii) the notion of observable electric potential measured with reversible electrodes; and (iii) the thermodynamics of irreversible processes. The electric potential, the electric charge density, and the Nernst−Planck−Poisson formalism are reviewed in this work. The properties of the new formalism are evidenced by applying it to MgCl2−H2O solutions.

2721polar species, either in bulk water or at an aqueous interface, and (2) those which are dependent on the electrostatic self-energy of a polar or charged group. As the simplest example of the first class, consider the interaction of two spherical charges well separated in bulk liquid. From continuum electrostatics, this interaction is given by Coulomb's law as W = (q1q2)/trlz where ql and q2 are the charge magnitudes, t is the intervening dielectric, and rI2 is the separation of the charge centers. Assuming that charges q1 and q2 were not derived to explicitly take into account the dielectric constant of the water used in the simulation, the error introduced by using a TIP4P with a dielectric constant of 60 in the simulation will be 33%. Examples of problems of biological interest which are governed predominantly by electrostatic interaction energies include shifts in pK's of surface residues on mutation and association rates of substrates with enzymes. The simplest example of the second class of properties is the free energy of transfer of an ion from water to a nonaqueous environment. From continuum electrostatics the electrostatic component of this free energy is given by the Born expression W = q2/(2a)[ l / t il/t,] where a is the radius of the cavity formed by the ion in the two media and where ti and e, refer to the dielectric constants of the nonaqueous environment and of water, respectively. For the transfer of such an ion from water to a uniform dielectric with ti = 4, the error in free energy of transfer by using a water with a dielectric constant of 60 is only 1.7%. Examples of properties of biological or chemical interest which can be largely governed by electrostatic self-energies of charged or polar groups include transfer free energies, desolvation of charged or polar substrates on binding to enzymes, and protein folding. The example given above used ti = 4 to suggest an ideal protein interior. Thus interaction-energy properties but not solvation free energy properties will be sensitive to the use of a water model with a dielectric constant which is 60. It is worth making a final point concerning biological or chemical simulations which employ explicit water models. To obtain the results presented here and in other dielectric simulations, a reaction field has been introduced to account for the continuum beyond the cutoff used in the simulation. The dielectric properties of the model under study change considerably if such a convention is not introduced. In simulations of proteins in water, reaction fields have not to date been introduced. As such, the dielectric constant of the waters in such simulations is undetermined.In conclusion, our results indicated that the free energy method can give results comparable to the induced polarization method, though it produces 2-3 times the standard error when both are analyzed using block averages. Values for the dielectric constant of TIP4P determined by the free energy method and the polarization method are slightly higher than those reported for compara...

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The preparation of new cation-exchange membranes from polymer composites based on poly(vinylidene fluoride), sulfonated polystyrene-co-divinylbenzene, and antimonic acid is reported. The thermal properties of the composites have been characterized by differential scanning calorimetry. Values of the transport number of protons in the membranes were obtained from the observable electric potential. It is defined from the potential difference measured between the electrodes reversible to one of the constituent ions in equilibrium with the system. When compared with Nafion cation-exchange membranes, the membranes described in this work exhibit interesting proton transport properties that could make them suitable as polymer electrolytes in fuel cells. © 2001 The Electrochemical Society. All rights reserved.

New transport equations for the thermoelectric phenomena have been deduced. All of the variables in this formulation are observable quantities. The limitations of the usual formulations, which work with nonobservable quantities, have been overcome. The electric potential can be measured by using auxiliary probes which connect the electronic conductor to a potentiometer. This observable electric potential depends on the nature of the probes but not on the room temperature where the potentiometer is placed. Also, we emphasize that absolute values for the thermoelectric power are in contradiction with the thermodynamic limitation of measuring electric potential differences in these systems. Therefore, the thermoelectric powers calculated either through the Thomson coefficient or in reference to a superconductor cannot be absolute quantities.