Chemistry

Whole Numbers for Half Cells?

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Science  15 Jun 2007:
Vol. 316, Issue 5831, pp. 1543
DOI: 10.1126/science.316.5831.1543c

Electrochemical reduction potentials in solution are generally measured and tabulated relative to a chosen reference reaction at the opposite electrode. Leib et al. have taken a step toward formulation of an absolute scale through gas-phase cluster experiments. They induced collisions between electrons and aqueous clusters of Ru3+ hexaammine ions, mass-selected to correspond to a bulk concentration of 1 M, and then they measured the energy dissipated upon electron capture by tracking how many water molecules evaporated from the cluster. This value in turn could be corrected for solvation free energies of reactant, product, and free electron to yield an estimate of solution-phase reduction energy. The authors note that although a solvated electron may still differ substantially from a charge transferred directly through a metal electrode, the cluster method includes molecular solvent-solute interactions that are otherwise very challenging to model. — JSY

J. Am. Chem. Soc. 129, 10.1021/ja067794n (2007).

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