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Kinetic equilibrium of chemical reaction

  1. Jan 7, 2015 #1
    I was thinking about this:

    Let's consider a dissociation of some chemical that can run in both directions:
    [itex]AB\rightleftharpoons A^{+}+B^{-}[/itex]
    Dissociated form is soluble in a solvent and undissociated form is not - it precipitates.
    Then the reaction proceeds to the left much faster than to the right, because dissociated form possesses much more reaction "surface" (it is dissolved) than a clot (clot reacts only on its surface).
    Also a reaction equilibrium moves almost entirely to the left, because reaction conditions (matter phase) differ from one reaction's side to another. Also the reaction equilibrium does not reflect the stability of reactants resp. products, so it's kinda false (or kinetic) equilibrium.

    Is this relevant idea in fact? Can some clot placed inside solvent dissociate but dissociated form does almost not exist in the solvent because of this?
    Or is this true - if any chemical cannot be dissolved by a solvent, it can be neither dissociated by a solvent?
  2. jcsd
  3. Jan 7, 2015 #2


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    Staff: Mentor

    While you are right that solids react only on the surface, it doesn't follow that the precipitation reaction is much faster.

    For a weakly soluble salts - yes. But of well soluble ones - no.

    Equilibrium for such a reaction is called a solubility product. Sometimes it is pretty low (predicted Ksp for PtS is something like 10-76, measured Ksp for AgI is something like 10-18), sometimes it is much, much larger (something like 25 for NH4Cl).
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