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Homework Help: Calculating cell potentials

  1. Oct 20, 2009 #1
    1. The problem statement, all variables and given/known data

    Calculate the potential of a Zn^2+/Zn and Ag^1+/Ag couple.

    2. Relevant equations

    Zn^2+ + 2e^1– ⇌ Zn E= –0.76 V
    Ag^1+ + e^1– ⇌ Ag E= +0.80 V

    3. The attempt at a solution

    First I know to multiply the silver half reaction by two so that each half reaction has two electrons. Then I flip the zinc reaction and switch the sign of its energy. Then, I added the two energies to get a cell potential of 1.56V. However, my homework is telling me that this is incorrect. I can not think of any reason why that is so. Any suggestions? Any help would be much appreciated.
  2. jcsd
  3. Oct 21, 2009 #2


    User Avatar

    Staff: Mentor

    E is not energy. You don't need to balance reaction to calculate potential. You don't flip the reaction - direction doesn't matter, both oxidation and reduction are both taking place at exactly the same potential.

    All that being said, 1.56 looks fine to me... I can be missing something - it happens, especiall early in the morning - but I think it is OK.

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