What is the Default Equilibrium Constant for Chemical Reactions?

[Nikitin]

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)=K1^0.5

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?

 

[DrDu]

There is no general default. Usually you have to give the reaction equation along with the equilibrium constant.

 

[Borek]

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.