Notes
Slide Show
Outline
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Electrochemistry
  • The study of the interchange of chemical and electrical energy.
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Review of Terms
  •   oxidation-reduction (redox) reaction:  involves a transfer of electrons from the reducing agent to the oxidizing agent.


  •   oxidation:  loss of electrons


  •   reduction:  gain of electrons
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Half-Reactions
  • The overall reaction is split into two half-reactions, one involving oxidation and one reduction.
  • 8H+ + MnO4- + 5Fe2+  ®  Mn2+ + 5Fe3+ + 4H2O
  • Reduction: 8H+ + MnO4- + 5e-  ®  Mn2+ + 4H2O
  • Oxidation:  5Fe2+  ®  5Fe3+ + 5e-
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Galvanic Cell
  • A device in which chemical energy is changed to electrical energy.
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Anode and Cathode
  • OXIDATION occurs at the ANODE.
  • REDUCTION occurs at the CATHODE.
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Cell Potential
  • Cell Potential or Electromotive Force (emf):  The “pull” or driving force on the electrons.
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Standard Reduction Potentials
  • The E° values corresponding to reduction half-reactions with all solutes at 1M and all gases at 1 atm.
  • Cu2+ + 2e-  ®  Cu           E° = 0.34 V vs. SHE
  • SO42- + 4H+ + 2e-  ®  H2SO3 + H2O
    •       E° = 0.20 V vs. SHE
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emf and Work
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Free Energy and Cell Potential
  • DG° = -nFE°
  • n = number of moles of electrons
  • F = Faraday = 96,485 coulombs per mole of electrons
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Concentration Cell
  • . . . a cell in which both compartments have the same components but at different concentrations.
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The Nernst Equation
  • We can calculate the potential of a cell in which some or all of the components are not in their standard states.
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Calculation of Equilibrium Constants for Redox Reactions
  • At equilibrium, Ecell = 0 and Q = K.
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Batteries
  • A battery is a galvanic cell or, more commonly, a group of galvanic cells connected in series.
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Fuel Cells
  • . . . galvanic cells for which the reactants are continuously supplied.
  • 2H2(g) + O2(g)  ®  2H2O(l)
  • anode:  2H2 + 4OH-  ®  4H2O + 4e-
  • cathode:  4e- + O2 + 2H2O  ®  4OH-
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Corrosion
  • Some metals, such as copper, gold, silver and platinum, are relatively difficult to oxidize.  These are often called noble metals.
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Electrolysis
  • . . . forcing a current through a cell to produce a chemical change for which the cell potential is negative.
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Stoichiometry of Electrolysis
  • How much chemical change occurs with the flow of a given current for a specified time?
  •       current and time ® quantity of charge ®
    • moles of electrons ® moles of analyte ®
    • grams of analyte