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Equilibrium Frustration.

  1. Aug 27, 2005 #1
    Equilibrium Frustration.......

    Ive been going over a chem paper and cannot seem to get any of the multiple choice given answers,

    the question is as follows,

    The free energy change for the formation of the complex ion [tex] AlF_6^3-[/tex] is -140. kJ at 25ºC. What is the equilibrium constant, K, for the reaction?

    Ive got:

    deltaG = -RT InK


    -140 = -(8.3145)(298.15) InK


    InK = -140 + (8.3145)(298.15)

    InK = 2338.0

    but this gives a value of K=0, which cant be correct, or if it is, the answer does not appear in the choices in my paper.

    Any ideas,

    Can anyone see where im going wrong?

    Thanks for your time.
  2. jcsd
  3. Aug 27, 2005 #2


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    Match the units you use.
    The value of the gas constant here is in Joules/(K*mol)
    In the left hand side of the equation you used the value of deltaG in Kilo Joules.
  4. Aug 27, 2005 #3
    Like Sid said, ALWAYS USE UNITS! UNITS! UNITS! The problem you are having is easy to spot when you simply use units.
  5. Aug 28, 2005 #4


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    And in addition to the problem with the units, how do you get K=0 from ln(K) = 2338 ?
  6. Aug 30, 2005 #5
    I got k=0 because,

    [tex] In(K) = 2338[/tex]
    e^In(K) = K
    e^2330 = 0


    I relooked over the problem, and it seems that i was simply not rearranging the values correctly. (Boy, did I feel super dopey!)
    I ended up with the right answer in the end.
    K = 3.5*10^25
    I think it was from memory.

    Thanks for the help everyone.
    Last edited: Aug 30, 2005
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