Talk:Equilibrium constant

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Isn't it K=[(C^n)(D^p)]/[(A^k)(B^m)] ?

I do not know who wrote this but I agree about that. I'm going to correct. Ange Blanc

[edit] units

can any one write something about the units of the reaction constant and how they are generated?

If you learned anything about equilibrium, you should know that equilibrium constants don't have units. No offense meant, but thats the one thing my teacher seemed to think was important about equilibrium, so I guess I have it deeply ingrained. Kr5t 02:41, 29 March 2006 (UTC)

I've been taught otherwise. Equilibrium constants can have units; in fact, they only don't if the equilibrium reaction in question involves the same number of moles on both sides (e.g. A+B->C+D has a Kc with no units, but A+B->4C involves a Kc with units). The units of Kc can be worked out simply by the relevant equation: for instance, in the reaction expressed as A+B->4C, Kc = [C]^4 / [A][B], and therefore its units are mol^2•dm^-6. - (Anonymous), 17 May 2006

Im sorry but anonymous above is actually incorrect. The equilibrium constant is always dimensionless because you devide each term by the standard state, effectively "cancelling the unit." I would refer you to "Atkin's Physical Chemistry", by Peter Atkins (Professor of Physical Chemistry at the University of Oxford) which i believe is the standard text for 1st year chemistry undergradutes. - (Markus), 28 July 2006

An equilibrium constant can be expressed as being dimensionless (K^o, or simply K): however, it is more usually referred to in terms of K_c or K_p, both of which can have dimensions [1]. This approach avoids having to use activity coefficients or fugacities, which are essential for the dimensionless approach (read Atkins more carefully!) Physchim62 (talk) 13:40, 28 July 2006 (UTC)

-- I agree. Each concentration should be divided by standard concentration, in the same units as the concentration. if the concentrations are in mols/liter (say), and the standard conc is 1 mol/liter, then the division has no numerical consequences, but it DOES get rid of the units. However,if the concentrations happen to be in molecules per cubic Angstrom, if you're a molecular simulation person :), then the standard concentration of 1 mol/liter needs to be included explicitly and its numerical value is something like 1 molecule/1660 cubic angstroms. So this WILL change the numerical value of K (compared to omitting it), and it will, again, get rid of the units. I think this issue is worth getting right in so widely used a widely-used reference site as Wikipedia!

[edit] Merge with Chemical equilibrium

This really oughtta merge with Chemical equilibrium, and with solubility equilibrium, and with an added section about solubility product constant, one of t he more special equilibrium constants since it doesn't involve the reactants.

[edit] Graph

The graph in this article is useful however it is slightly misleading. As a student we mostly study Gibb's free energy (and its relation to the Equilibrium constant) with spontaneous reactions of which this graph represents none. It would be nice to show the lower side of this curve too in order to allow for a better perception of the concept.