chem exam

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chem exam
2012-04-30 12:50:59
chem exam

chem exam
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  1. to be spontaneous the change in S must be
    Greater than 0
  2. Things that can increase entropy are:
    • 1. increase in temp
    • 2. volume increase
    • 3. moving particle increase
  3. Processes that can increase entropy
    • 1. solid/liquid -> gas
    • 2. solid -> liquid
    • 3. gas molecule increase
  4. properties of the system that depend only on its present state
    state functions
  5. change H +
    change S -
    • change G +
    • always nonspontaneous
  6. change H -
    change S +
    • change G -
    • always sponstaneous
  7. change H -
    change S -
    spontaneous @ low temps
  8. change H +
    change S +
    spontaneous @ high temps
  9. what is a voltaic or gavanic cell?
    * an electrochemical cell in which a spontaneous rxn generates an electric current

    * Has 2 half-cells that are electrically connected
  10. What is the purpose of a salt bridge?
    to allow the flow of ions while preventing the mixing of the different solutions that would allow direction rxn of the cell reactants
  11. which "ode" is oxidation?
  12. which "ode" is reduction?
  13. directions of the "odes"
    • anode gives up electrons
    • flows to cathode
  14. Which "ode" is + and which is -?
    • Cathode: +
    • Anode: -
  15. Rules for describing voltaic cell short hand style:
    • 1. anode(oxidation) on left, cathode(reduction) on right
    • 2. vertical line to indicate phase boundary (solid and solution)
    • 3. 2 vertical lines for salt bridge
  16. EMF
    Electromotive Force
  17. If E is positive:
    rxn is spontaneous
  18. equation for standar E:
  19. Which half-rxn should you flip signs on?
    cally said the most negative one
  20. what is coulombs x volts?
  21. What is coulomb?
    the amount of electric charge transported by a steady current @ 1 atm
  22. When is the Nernst equation used?
    to calculate cell potentials at non-standard states
  23. Explain Electroplating
    • * a plating process in which metal ions in a solution are moved by an electric field to coat an electrode.
    • * electrical current reduces cations of a desired material from a solution and coats a conductive object with a thin layer of material, such as a metal.
    • * Used for: abrasion and wear resistance, corrosion protection, lubricity, aesthetic qualities
  24. What is corrosion?
    • * the gradual destruction of material, usually metal, by chemical reaction with its environment
    • * electrochemical oxidation of metals in reaction with an oxidant such as oxygen.
    • *Rusting, the formation of iron oxides
  25. Define electrolysis
    a method of using a direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction