Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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


    User Avatar
    Homework Helper
    Gold Member

    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


    User Avatar
    Staff Emeritus
    Science Advisor
    Gold Member

    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
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?

Similar Discussions: Equilibrium Frustration.
  1. Chemical Equilibrium (Replies: 3)

  2. Gas Equilibriums? (Replies: 5)

  3. Time to equilibrium (Replies: 6)

  4. Chemical equilibrium (Replies: 4)

  5. Equilibrium Constants (Replies: 4)