Electrode Potential Half Reactions

Does flipping a reaction as written change the sign of the value of E or is it a completely different value? 


For example if I have the value for the half reaction $\ce{Cl2 + 2e- -> 2Cl-}$ but need the value for the opposite reaction ($\ce{2Cl- -> Cl2 + 2e-}$), do I just put a negative sign and treat it like $\Delta H$ values? 




Yes, you are correct - just flip the sign. As quoted from [the venerable UC Davis ChemWiki](http://chemwiki.ucdavis.edu/Analytical_Chemistry/Electrochemistry/Voltaic_Cells/The_Cell_Potential):



> 
> To determine oxidation electrodes, the reduction equation can simply be flipped and its potential changed from positive to negative (and vice versa).
> 
> 
> 


They give the value for your (forward) reaction as +1.358 V, so for the reaction in question, you'll use **-1.358 V**.


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