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Default equilibrium-constant?

  1. Dec 12, 2012 #1
    Let's say we have the reaction 2H2 + O2 -> 2H2O. The equilibrium constant for this reaction then is: K1=[H2O]2]/([H2]2*[O2]).

    But the reaction can also be written as H2 + 0.5O2 -> H2O, and with the equilibrium constant becoming K2 = [H2O]1]/([H2]1*[O2]0.5)=K10.5

    This phenomena with the coefficients goes generally for all reactions. So, what K is the default one? Is it the one where most coefficients are 1 (K2), or is it when all coefficients are at their smallest, while remaining integers (K1)? Or something else?
  2. jcsd
  3. Dec 12, 2012 #2


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    Science Advisor

    There is no general default. Usually you have to give the reaction equation along with the equilibrium constant.
  4. Dec 12, 2012 #3


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    Staff: Mentor

    Most often you will see the equilibrium constant for the properly balanced reaction equation - that is, with all coefficients being the smallest possible integer numbers. So when there is no other information I would assume value given is K1. Serious sources of equilibrium constants usually define the convention used, to make the information unambiguous.

    Which basically boils down to what DrDu wrote earlier.
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