Chemical Forums

Chemistry Forums for Students => Undergraduate General Chemistry Forum => Topic started by: hellohello on October 21, 2008, 05:38:13 PM

Title: determining concentrations from absorbance change
Post by: hellohello on October 21, 2008, 05:38:13 PM

Does anyone know how to determine the final concentration of all reactants and products at equilibrium. I know i have to use keq...but i am totally lost. Any help would be appreciated!

Title: Re: determining concentrations from absorbance change
Post by: Borek on October 21, 2008, 05:54:53 PM

Please elaborate.

Title: Re: determining concentrations from absorbance change
Post by: hellohello on October 21, 2008, 06:20:58 PM

I am trying to estimate the final concentration for all reactants and products in a reaction mixture at equilibrium and determine the keq

The reaction is  NADH + Pyruvate <---> NAD+ + lactate
Initial                y           z                   0           0
Change            -x         -x                   +x         +x
Equilibrium        y-x        z-x                   x           x

ΔAtotal = ΔANADH + ΔApyruvate = εNADHxl + εpyruvatexl

          [NAD+][lactate]
Keq = ----------------
        [NADH][pyruvate]

Initial Concentrations:
[NADH] = 0.9mM
[pyruvate] = 2.5 mM

ΔAtotal =.741

Title: Re: determining concentrations from absorbance change
Post by: enahs on October 21, 2008, 09:32:14 PM

To be   :delta:A would be Helmholtz energy, which is what I doubt you mean.

So what are your  :delta:A's and ε represent (I can list so many things for ε it is silly)?

Title: Re: determining concentrations from absorbance change
Post by: Borek on October 22, 2008, 03:02:26 AM

I suppose s/he means absorbance.