Articles you may be interested inBinary nucleation in acid-water systems. II. Sulfuric acid-water and a comparison with methanesulfonic acid-water J. Chem. Phys. 94, 6842 (1991);The rate of solution of cadmium in sulfuric acid has been measured as a function of the hydrogen overvoltage at the electrode surface. The rate was found to be constant at a given potential, independent of the concentration of sulfuric acid used. The rate increases with the electrode potential in accordance with ~he theory of Kimball. From the dependence of the rate on the speed of stirring, and also from the behavior on varying the potential, it is concluded that the solution process is diffusion controlled. The effect of surface inhomogeneities was too great to permit an evaluation of the absolute rate.By taking into account the London "dispersion" forces and the structural characteristics of a liquid system, an equation for the change of rotivity per mole of dipole solvent in unit volume for liquid solutions is obtained which has the same form as the equation obtained by Beckmann and Cohen for a mixture of gases that are perfect except for dipole interaction, namely,
S=G(OI., {3, 'Y)+K-yP-y.This is due to the fact that the polarization term arises from the integration over the angles of orientation alone. The constants, G(OI., (3, 1') and K-y have, of course, a new significance in the present work.
The theory of absolute reaction rates applied to electrode processes leads to the equation s=(kT/h) exp (−ΔF*/RT) exp (αVF/RT)for the specific rate of discharge of ions. The question arises as to whether V should be the actual potential at the electrode or only the overvoltage. In the case of hydrogen ion discharge, it is found experimentally that the overvoltage should be used. On the other hand, the theory in its simplest form requires V to be the total potential. This paradox can be resolved by postulating the existence of two different electrical double layers at the electrode surface, and two corresponding energy barriers over which the protons must pass. Provided that the barrier nearer the electrode is the higher, the overvoltage is essentially established across this layer, while the variation in equilibrium potential caused by variations in the hydrogen ion concentration of the solution is established across the outer double layer. Since the rate of discharge is determined by the potential difference across the inner double layer, the rate is determined by the overvoltage, and not by the total potential. The nature of these two energy barriers is also discussed. Both barriers may correspond to transfer of protons from water molecule to water molecule, or one may correspond to the actual discharge process in which a neutral hydrogen atom is formed. It does not yet seem to be possible to decide between these two alternatives, either theoretically or experimentally, but it seems most probable that both barriers correspond to proton transfers from water molecule to water molecule.
The problem of simultaneous conduction and diffusion through a constrained diffusion layer is discussed. An exact solution is obtained for the case of an ideal dilute solution containing only two ionic species. The special case of divalent ions diffusion into a uni-divalent electrolyte is also solved by numerical methods. It is shown that for diffusion layers of thicknesses of the order of 50μ the potential drop across the layer for currents of the order of magnitude of 100 milliamperes per sq. cm is less than one millivolt. It is therefore legitimate to neglect the diffusion potential in comparison with the double layer potential at an electrode surface.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.