Redox problems
In MINTEQ, there
are separate components to represent the oxidation states of interest.
For example, both Fe2+ and Fe3+ are included as components.
In addition, there are mock species that are defined to represent the activity
ratio of two members of a redox couple. The two most common ways of including
redox problems in MINTEQ are the following:
-
The redox potential (Eh) or electron
activity (pe) is known. Calculate the distribution between different members
of a redox couple. First, choose Redox – Specify
redox couples. Locate the redox couple of your choice from the scroll-down
menu. You will obtain the log K value and the reaction enthalpy defined
on the basis of the stoichiometry, which is also displayed for each redox
couple. If you change these constants the changes will only be made to
this particular problem. If the components of the redox couple had not
previously been added, they will be added to the component list with a
total concentration of 0. When you click Add,
the redox couple will be added to the list of fixed species. The redox
couple can be removed by deleting it from this list. Second, specify the
sum of the total concentrations of the redox components by writing the
value to either of the relevant redox components on the list of components
(it doesn’t matter which one you choose). Third, choose Parameters
– Specify pe and Eh, or press CTRL-E, and choose the first (fixed
pe) or second (fixed Eh) option. You are prompted to supply the value for
pe or Eh.
-
The total concentrations of both
redox components are known. Calculate the pe or Eh value that matches the
known distribution of redox components. First, choose Redox
– Specify redox couples. Locate the redox couple of your choice
from the scroll-down menu. You will obtain the log K value and the reaction
enthalpy defined on the basis of the stoichiometry, which is also displayed
for each redox couple. If you change these constants the changes will only
be made to this particular problem. If the components of the redox couple
had not previously been added, they will be added to the component list
with a total concentration of 0. When you click Add,
the redox couple will be added to the list of fixed species. The redox
couple can be removed by deleting it from this list. Second, specify the
total concentration of both redox components, unless you haven’t already
done so.