# What drives the redox reactions in a standard hydrogen electrode?

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 '18 at 13:16