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General Equation for the Relation Between the Polarographic Half-Wave Potential and Substituent Effects

  • Petr Zuman

Abstract

For a reversible oxidation-reduction process, the half-wave potential (corrected for the quotient of the diffusion coefficients of the oxidized and reduced forms) is proportional to the equilibrium constant K of the reaction
$$Ox+ne\rightleftharpoons \operatorname{R}ed$$
$$K=\frac{\left[ Red \right]}{\left[ Ox \right]}$$
namely,
$$-E_{{1}/{2}\;}^{0}=\frac{RT}{nF}\ln K$$
(1)
Since
$$RT\ln K=\Delta {{F}^{\circ }}$$
(2)
where ΔF°is the change in the standard free energy, it follows that
$$-nFE_{{1}/{2}\;}^{0}=\Delta {{F}^{\circ }}$$
(3)
For half-wave potentials of irreversible systems, the relationship(4) has been derived:1–5
$${{E}_{{1}/{2}\;}}=\frac{RT}{\alpha nF}\ln 0.87k_{\int }^{0}\sqrt{\frac{{{t}_{1}}}{D}}$$
(4)
where R is the gas constant, T is the absolute temperature, α is the transfer coefficient, n is the number of electrons transferred in the electrode process, F is the faraday (96,500 coulombs), k 0 f is the rate constant of the heterogeneous electrode process, t1 is the drop time, and D is the diffusion coefficient.

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Copyright information

© Plenum Press 1967

Authors and Affiliations

  • Petr Zuman
    • 1
  1. 1.Heyrovský Institute of PolarographyCzechoslovak Academy of SciencesPragueCzechoslovakia

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