[CHM 112] Which Delta G

[Andrew J. Pounds]

On 07/12/13 18:22, wrote:
> Dr Pounds,
> I have a question with regards to the Delta G circle = -RT ln K equation,
> In number 82 of Burdge, you used Delta G= -RT ln K to solve, how do we know when to use either equation for Delta G circle or delta G.
>
> Thank you

I apparently left off the superscript zero when I wrote that solution.  
Here is the rule of thumb you need to remember -- if you are looking for 
an equilibrium constant then you are looking for where the Gibbs Free 
Energy function has a slope of zero ($\Delta G$= 0}.

$\Delta G = \Delta G^{\circ} + RT lnQ$

at equilibrium

$0 =  \Delta G^{\circ} + RT lnK$

or

$\Delta G^{\circ} = -RT lnK$

So basically -- if you are looking for an eqauilibrium constant you will 
want to calculate $\Delta G^{\circ}$ using the thermo tables and then 
find K.


-- 
Andrew J. Pounds, Ph.D.  (pounds_aj at mercer.edu)
Professor of Chemistry and Computer Science
Mercer University,  Macon, GA 31207   (478) 301-5627
http://faculty.mercer.edu/pounds_aj

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