-438 kJ/mol is the free energy change of lactate oxidation by Fe3+ under non-standard conditions assuming that:
C3H5O3- + 12 Fe3+ + 3 H2O -----> 3 CO2 + 11 H+ + 12 Fe2+
T=25 degree centigrade
Carbon dioxide is in equilibrium with atmospheric CO2
Fe3+ is in equilibrium with Fe(OH)3 (s)
Note for Fe(OH)3, Ksp=10^-38
Ksp is the equilibrium constant
Would the following changes make the overall free-energy change more or less favorblae for the overall reaction described above? (Indicate whether the free energy change is sensitive or insensitive to these differences by calculation of free energies):
1. Raise pH of solution to 8.0
2 . Lower Lactate activity to 10^-5 M
3. Add FeCl3 while maintaining solution pH at 7.0
4. Allow CO2 to build up in solution to equilibrate with 10^-2 atm CO2 while maintaining pH at 7.0
5. Raise the solution temperature to 35 degree C. (Describe how this would be done, but please don't solve equations).
The solution shows how to analyze the effect of changing certain conditions on the free energy of a non-standard cell.