(gen chem) whats the difference ?

[swamprat]

I remember seeing this formular: EMF = Ecat -Eanod

But now I also see EMF = Eox + Ered.

Did I just make that first equation up? I def saw it somewhere I can't find it in my review book though.

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[futuredoctor10]

I remember seeing this formular: EMF = Ecat -Eanod

But now I also see EMF = Eox + Ered.

These are just two conventions for writing the EMF formula but both work.

If you write the two equations (half-reactions) so that one is undergoing reduction and one is undergoing oxidation, and you change the value of E by inverting the sign, then you can just add the electric potentials.
** if reactions are written so that they are undergoing reduction (convention), you would flip the reaction [so it will undergo oxidation from L-->R] AND flip the sign.

If you identify two half-reactions but DO NOT flip the reaction/sign, then you need to use EMF = Ecat -Eanod.

Does that make sense?