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When looking at standard hydrogen potential electrode diagrams in the case of a negative standard reduction potential for the other half cell, I came across one part that does not make sense to me: (image from chemistry libre texts)

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Unless I'm reading it wrong, it appears that hydrogen gas is being added to the system at 1 atm. Why is hydrogen gas being added if it does not participate in the reduction reaction of protons in solution? It seems to me that adding hydrogen gas will hinder the process by pushing the chemical equilibrium to the left.

NickC64
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    It is not specific for the hydrogen electrode. An electrode potential depends on activities of both oxidized and reduced forms, regardless of the direction of the net reaction. – Poutnik Jul 19 '21 at 05:39
  • There is a good explanation and diagram here, https://www.chemguide.co.uk/physical/redoxeqia/introduction.html – porphyrin Jul 19 '21 at 07:43
  • @porphyrin From what I interpret from the article, would the diagram I posted be misleading as to how the standard hydrogen electrode would be used? It appears to me that minimal amounts of current should be allowed to flow through the voltmeter in order to truly measure the standard reduction potential of the other half cell. – NickC64 Jul 19 '21 at 20:35

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