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2011-12-10 23:46:55

Chapter 20 Electrochemistry
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  1. redox reaction:
    oxidation-reduction reaction
    a reaction in which certain atoms undergo changes in oxidation states
  2. oxidation
    a process in which a substance loses one or more electrons: increasing in oxidation state
  3. reduction
    a process in which a substance gains one or more electrons: reducing in oxidation state
  4. oxidizing agent or oxident
    the substance that is reduced and thereby causes the oxidation of some other substance in an oxidation-reduction reaction
  5. reducing agent or reductant
    the substance that is oxidized and thereby causes the reduction of some other substance in an oxidation-reduction reaction
  6. oxidation numbers
    a positive or negative whole number assigned to an element in a molecule or ion on the basis of a set of formal rules; to some degree it reflects the positive or negative character of that atom
  7. half-reaction
    an equation for either an oxidation or reduction that explicitly shows the electrons involved
  8. cathode
    an electrode at which reduction occurs
  9. anode
    an electrode at which oxidation occurs
  10. voltaic cells (galvanic)
    • a device in which a spontaneous oxidation-reduction reaction occurs with the passage of electrons through an external circuit:
    • electrons flow from the anode through the external circuit towards the cathode
  11. salt bridge
    • a u-shaped tube containing an electrolyte solution such as NaNO3(aq) whose ions will not react with other ions in the voltaic cell or with the electrodes:
    • allows ions to migrate between half cells:
    • anions towards the anode, cations toward the cathode
  12. cell potential (E0cell)
    • the potential difference between the cathode and the anode in an electrochemical cell
    • measured in Volts 1V=1 J/C
    • Also called electromotive force (emf)
  13. electromotive force (emf)
    a measure of the driving force, or electrical pressure, for the completion of an electrochemical reaction.
  14. Nernst Equation
    An equation that relates the cell emf to the standard emf and the reaction quotient,Q.

    E = E0 - (RT/nF) ln Q
  15. Concentration cells
    a voltaic cell containing the same electrolyte and the same electrode materials in both the anode and cathode compartments. The emf of the cell is derived from a difference in the concentrations of the same electrolyte solutions in the compartments.
  16. Faraday's constant (F)
    the magnitude of charge of one mole of electrons = 96,500 C/mol
  17. Using the half reaction method to balance redox reactions:
    Divide the equation into one oxidation half-reaction and one reduction half-reaction.

    • Balance each half reaction:
    • 1st: balance elements other then O or H
    • 2nd: balance O by adding H20
    • 3rd: balance H by adding H+
    • 4th: balance charge by adding e-

    Multiply half-reactions by integers as needed to make the number of electrons lost equal to number gained in each half-reaction.

    Add half-reactions, and simplify by canceling species appearing on both sides of the combined equation.

    Check to make sure atoms and charges are balanced.