In oxidation-reduction reactions, electrons transfer. Electron transfer requires voltage {potential, reaction}. Oxidation-reduction half-reactions have potentials. Total oxidation-reduction reaction potential is sum of half-reaction potentials.
level
Electronegative atoms have high reduction potentials.
calculation
Cell standard potential depends on half-reaction potentials and balanced equation. From balanced equation, separate reduction and oxidation half-reactions. Tables have half-reaction reduction potentials at 25 C. Subtract reduction potential for oxidation half-reaction from reduction potential for reduction half-reaction to find chemical-reaction potential.
spontaneity
If oxidation-reduction chemical-reaction potential is greater than zero, chemical reaction is spontaneous. If reduction potential is more than oxidation potential, ionization potential is higher, hydration energy is lower, and sublimation energy is more.
equilibrium
When oxidation-reduction reaction is complete, potential is zero.
Half-cell reduction-reaction voltage depends on oxidized and reduced concentrations, temperature, and number of electrons transferred {Nernst equation}. V = V0 - R * T / (n * ln([Co] - [Cr])), where V is reaction potential, V0 equals standard unit cell potential, R is gas constant, T is temperature, n is number of electrons transferred, Co is oxidized-ion concentration, and Cr is reduced-ion concentration.
Activation energy comes from electric field and from temperature.
valence charge
Electrode voltage is V = V0 + R * T * ln(K / (z * F)), where V is voltage, V0 is standard potential, R is gas constant, T is temperature, K is equilibrium constant, z is absolute value of transferred charge {valence charge}, and F is 1 Faraday. Therefore, exp(-V / (R*T)) = K / (z * F) and K = z * F * exp(-V / (R*T)). Standard potential is at concentration 1 M, pressure 1 atmosphere, and temperature 25 C. Solids have concentration = 1. Voltage is always positive. If V > 0, reaction is spontaneous. At equilibrium, voltage = 0 and current = 0.
5-Chemistry-Inorganic-Oxidation-Reduction
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Date Modified: 2022.0225