Redox_Potentials_and_Equilibria_S11

Redox_Potentials_and_Equilibria_S11 - Redox Potentials and...

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1 Redox Potentials and Equilibria GLY 4241 - Lecture 11 Spring, 2011
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2 Equilibrium Treatments Free energy (ΔG = ΔH – TΔS) Using equilibrium constants Use of oxidation-reduction reactions Reactions written in half-cells
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3 Example Half-Cell Reactions Oxidation: Reduction: Full cell:
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4 Oxidation-Reduction Video
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5 Complicated Reaction
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6 Arbitrary Standard Measuring the absolute value of the potential for an ion to gain or lose an electron is impossible Therefore, an arbitrary standard is chosen:
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7 Standard Conditions This has an arbitrary standard potential (at standard conditions [H 2 ] = 1 atmosphere and 25 ° C) E ° = 0.00 volts E ° denotes standard potential
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8 Half-Cells in Terms of Standard Once a standard is chosen, all other half- cell reactions can be defined in terms of the standard Example:
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9 Is a Reaction Favorable? A table of electrode potentials (these are readily available) can be used to judge which reactions are thermodynamically favorable A reduced ion will react with any oxidized species less negative than itself
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10 Favorable Reaction Thus, uranium U 3+ will reduce tin Sn 2+
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11 Unfavorable Reaction Uranium cannot reduce magnesium
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12 Combining Half-Cells A reaction's potential difference can be found by combining two half cell reactions: Doubling a reaction does not change the potential Potential is an intensive variable
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Redox_Potentials_and_Equilibria_S11 - Redox Potentials and...

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