When to use standard potentials and when to balance

[Lucia H 2L]

What is the difference was between skeletal reactions that you have to balance by adding H+ and OH- vs skeletal reactions that you can jut copy down from the standard potentials page? In theory, a half reaction is a half reaction, right?

[Tanaisha Italia 1B]

I think that if the products have oxygen or hydrogens that are unaccounted for in the reactants then you would have to balance by adding H+ and OH-. Especially when it says something along the lines of:
1. Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in acidic solution.
or
2. Balance each of the following skeletal equations by using oxidation and reduction half-reactions. All the reactions take place in basic solution.

If the reaction is something simple, like Mg2- + 2e- -----> Mg, you don't need to add anything because there are no oxygens or hydrogens on either side.
If it is more complicated, and one side has an oxygen/hydrogen and the other does not, you have to add it:
Ex. 2ClO3- + 5e- -----> Cl2
You would have to balance this because 2ClO3- has 6 oxygens which have to be accounted for on the other side (by adding 6H20, the oxygen has to go somewhere)

[Kaileigh Yang 2I]

It's just like balancing an equation to complete it. Just remember to balance according to whether it is a basic or acidic solution.