Why can't we have half-reactions by themselves?

1 Answer
Truong-Son N.
Jul 11, 2016

Half reactions are said to have cell potentials that... well, are potential differences. You can't have a difference between x and nothing else. You need a y.

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 "0 V"; it is easier to be in reference to a voltage of "0 V" than an absolute cell potential of "4.44 V".

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