CHEMISTRY COMMUNITY

How come the anode rxn's Eº = +1.23 V and not -1.23 V? In the book the reaction is written O2 + 4H+ + 4e- → 2H2O with Eº = +1.23 V. Since they've switched the reaction here, why isn't it -1.23?

You don't have to switch the sign of Eº if when calculating Eºcell you always use Eºcathode-Eºanode.

If you prefer to use the method where you add the Eºcathode and Eºanode you must flip the Eºanode.

Dr. Lavelle discussed 2 methods to calculate Ecell. The first method is to use E^ocell = E^ocathode - E^oanode, and you wouldn't switch the signs for the E^o here. The second method is to add E^o of the two half-reactions together, and you would switch the sign for the oxidation reaction E^o because the standard reduction potential tables lists the reduction half-reactions.