Why can't we have half-reactions by themselves?
Half reactions are said to have cell potentials that... well, are potential differences. You can't have a difference between
So, each half-cell potential was itself measured with respect to either:
- the Standard Hydrogen Electrode (SHE),
- the Saturated Calomel Electrode (SCE),
or some other reference electrode. The SHE is quite common, and it was declared to have an arbitrary absolute cell potential of