Do these half-reactions have electrode potential that depends on pH?

[Dolphinsea14]

Do following half-reactions have electrode potential that depends on pH? I know H+ or OH- ions wouldn't be included in Nernst equation for these, but would pH affect chemical balance in these reactions, and therefore electrode potentials?
Br2+2e- -> 2Br-
Cl2+2e- -> 2Cl-
I2+2e- -> 2I-
S2O8+2e- -> 2SO42-?

 

[TeethWhitener]

Yes. You can google the Pourbaix diagrams for these species to find the dependence.

I know H+ or OH- ions wouldn't be included in Nernst equation for these, but would pH affect chemical balance in these reactions, and therefore electrode potentials?

This isn't quite true. At least for the halides, in water one of the stable species that is formed in highly oxidizing conditions is hypohalite, which entails reaction between the halide and water.

 

[Dolphinsea14]

I found this in a book (Inorganic Chemistry by Shriver and Atkins). It seems redox potential in these cases doesn't depend on pH.

 

[TeethWhitener]

Ok, yes for the Cl₂/Cl^- couple specifically, there is no dependence on pH. You can see this on the Pourbaix diagram for chlorine as a horizontal line at low pH and high voltage (it's easier to see in the bromine diagram):

But it's kind of a weird statement to make, because aqueous Cl₂ is not stable above pH 2 or so. It reacts with water to form HOCl, which gets deprotonated at high pH to give hypochlorite. Note that the redox potential for Cl^-/hypochlorite is dependent on pH.

 

[Borek]

In other words: there is no dependence on pH, just the reaction doesn't occur when the pH is high enough (so whole discussion becomes a moot).