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Disolution of an amount of Fe
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Topic: Disolution of an amount of Fe (Read 1018 times)
luicho
Frequent Contributor
Posts: 18
Disolution of an amount of Fe
«
on:
July 09, 2014, 05:29:19 PM »
Hello,
I'm trying to understand how phreeqc do this calculation:
Database sit.dat
Solution 1
REACTION 1
Fe(s) 1
1 micromoles in 1 steps
END
I'm trying to find what semi-reactions use phreeqc to calculate the final pE?
Does Phreeqc use the Nernst Equation to calculate the final pE?
pE= log_k/ne - 1/ne * log({red}/{ox})
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dlparkhurst
Top Contributor
Posts: 957
Re: Disolution of an amount of Fe
«
Reply #1 on:
July 10, 2014, 04:15:40 PM »
Yes, but not quite that way.
PHREEQC solves a set of mole balance and mass-action equations. For the system you are considering, PHREEQC would have the following equations:
Mole balance on H, O, Fe, and charge; and a set of mass action equations for OH-, Fe+3, FeOH+2, Fe(OH)2+, and so on.
The mass-action equations are effectively substituted into the mole balance equations, so you end up with 4 equations, and the 4 unknowns are pH, pe, a(Fe+2), and mass of water.
Now the mass-action equation for Fe+3 is your Nernst equation rearranged such that log K = .... . So the calculated pe is such that the Nernst equation will be satisfied. If you have multiple redox elements, the pe calculated from any of the appropriate Nernst equations will be the same.
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Disolution of an amount of Fe