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Question on chemical equilibrium

  1. Aug 28, 2015 #1

    Titan97

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    Gold Member

    1. The problem statement, all variables and given/known data
    The formation of cadmium complexes with Br- exhibits successive equilibrium constants such that log(k1)=1.56, log(k2)=0.54, log(k3)=0.05, log(k4)=0.37.
    Explain why k4 is greater than k3

    2. Relevant equations
    $$K=e^{\frac{-\Delta H}{RT}}\cdot e^{\frac{\Delta S}{R}}$$

    3. The attempt at a solution
    After reading chemical equilibrium from peter Atkins's chemical principles, I learned that larger values of K means the reactions is exothermic. (This can be said using the above equation).
    Larger value of K, could also mean that ##\Delta G## is strongly negative causing more products at equilibrium.
    This explains why some equilibrium constants are large. But this does not explain why K3<K4.
     
  2. jcsd
  3. Aug 28, 2015 #2

    Borek

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    I would try to analyze symmetry and electronic configuration of complexes involved to see if there are no indications to which one is more stable.
     
  4. Aug 28, 2015 #3

    Titan97

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    But no information about the structure of complex is given. (I think its tetrahedral)
     
  5. Aug 28, 2015 #4

    Borek

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    This is even more complicated, as cadmium ion is first complexed by water molecules, they are then replaced by Br-.

    In what context was this question asked? I mean - what is the thing you are learning now?
     
  6. Aug 28, 2015 #5

    Titan97

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    I am learning chemical equilibrium. But I know the basics about crystal field theory and coordinate compounds. So the reaction is about Br- replacing OH- in the complex. Its OK. I would like to learn about this. (I will post the solution given in the solution manual, I don't have it right now).
     
  7. Aug 29, 2015 #6

    Titan97

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    I got the solution manual @Borek , this is the equation given
    $$[CdBr_3(OH)_2]+Br^-\to [CdBr_4]^{2-}+3H_2O$$
    According to the author, "there is an increase in the number of particles and hence an increase in dissorderness. This is because of formation of a less restricted coordination sphere."
    Am I supposed to learn the equation or is there a general rule to be followed?
     
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