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Redox Reactions and standard emf calculations

  1. Mar 22, 2012 #1
    What is the equation I should be using for the following question:

    At 298K a cell reaction has a standard emf of +0.17V. The equilibrium constant for the cell reaction is 5.5 X 10^5. What is the value of n for the cell reaction.

    Grateful for anyone's help!
     
  2. jcsd
  3. Mar 23, 2012 #2

    Borek

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    Staff: Mentor

    What equations have you learned while studying redox potentials?
     
  4. Mar 24, 2012 #3
    E°cell = E°cathode - E°anode
    E°cell = (RT/nF)(lnk)
    E = E° - (0.0592/n)(logk)
     
  5. Mar 24, 2012 #4

    Borek

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    Staff: Mentor

    Why don't you just select the equation containing all known values and n? This is almost a simple plug and chug.
     
  6. Mar 25, 2012 #5
    The equation that should be most likely used is E = E°-(0.0592/n)(logk).
    I have the value for the standard emf = E°, and value of k.

    Do I assume E to be zero then? If I do so, then the solution should look like the following:
    0= E° - (0.0592/n)(logk)
    0= 0.17 - (0.0592/n)(log(5.5*10^5))
    0.17 = (0.0592/n)(log(5.5*10^5))
    n= (0.0592)(log(5.5*10^5)) / 0.17
    n= 1.9989
     
  7. Mar 25, 2012 #6

    Borek

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    Staff: Mentor

    Yes.

    When Q=K cell potential is zero.
     
  8. Mar 25, 2012 #7
    Thank you for the help!
     
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