# What is the actual voltage to the standard hydrogen electrode and why is it used?

Why is the standard hydrogen electrode chosen to be of 0 voltage, what is its actual voltage and how could that be calculated experimentally?

Also, why is it that we cannot measure the voltage or potentials of the range of electrodes and we must use the standard hydrogen electrode?

The voltage given for any reduction is totally meaningless in the absence of either a comparison to another reduction potential or an oxidation potential. Absolute energies are totally meaningless. Only differences matter.

As usual then, we need references. For example, heat of formation of standard Gibbs energy if formation are set to 0 for elements in their standard forms at standard state.

Likewise, for reduction potentials, we need a reference, and that reference if the standard hydrogen electrode, whose standard reduction potential is 0 by fiat. All other potentials can be determined by comparison.

• I see, but why is it that the "the voltage given for any reduction is totally meaningless in the absence of either a comparison to another reduction potential or oxidation potential" and why is it that "only differences matter". Dec 13, 2016 at 13:00
• Because absolute potential energies are the only thing that matter. That's how energy works. You can shift the scale however you like, but the differences are still the same and determine everything you want to know.
– Zhe
Dec 13, 2016 at 13:26
• @Zhe Well, then why don't we connect SHE to ground (zero potential) and measure the "actual" potential of SHE? We can use potentiometer or Wheatstone bridge to measure potential without any current. Feb 1, 2017 at 14:23
• @Zhe I'm saying is that - What is the standard potential of the reduction of $H+$? Feb 1, 2017 at 14:44
• That's not how reduction potentials work. They have those relative values because the corresponding oxidation potentials are also referenced to the same standard... You cannot just arbitrarily define a new standard like "ground" for these purposes.
– Zhe
Feb 1, 2017 at 14:57