In this video, the SHE half cell has two redox reactions occurring i.e.

$$\ce{2H+ (g) + 2e- <=> H2 (g)}\\ \ce{H2 (g) <=> 2H+ (g) + 2e-}$$

But how can a single half cell initiate the two reactions? In the video, e- are going into the platinum wire which react with the H+ in the aqueous solution, but where does the e- come from?

And how can $\ce{H2 (g)}$ randomly release two $\ce{e-}$ into the copper wire? Where did the $\ce{H2 (g)}$ get the energy to release the two $\ce{e-}$?

  • The short answer is that it doesn't. You need something (an oxidant) to pick up the electrons in such a way that the overall process of transferring electrons is favorable. Also, only the first reaction you wrote is a reduction. The other is an oxidation. – Zhe Oct 4 at 13:16

It is an equilibrium reaction, so the two reactions occur at the same rate and the net current is 0 (electrons are flowing in both directions). A net current will flow only if another half cell is connected.

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