NEed CHemIstry Help immeDiAtelY

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SoorajG1
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#1
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In hydrogen -oxygen fuel cells, my exam board (AQA) says that electrolysis occurs in these fuel cells. So I thought that ions are either oxidised or reduced in electrolysis to form atoms but in my revision guide it shows that hydrogen ATOMS are being REDUCED to make H+ IONS. WTF. here is the half equation-provided by the revision guide: h2->2H+ + 2e-.
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Kian Stevens
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No, the half equation shows the oxidation of an elemental dihydrogen molecule (H2) to form H+ ions, and some electrons are lost in this process. That isn't the reduction, but the oxidation.
This is a part of how these fuel cells work; I don't see the problem.

H2 molecules oxidise to form H+ ions, and the electrons from this process will produce a current.
The H+ ions pass through an electrolyte, where they recombine with the electrons lost to form H2 again (hence this time, hydrogen is reduced).
The H2 reacts with O2 to produce water.
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SoorajG1
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Okay but, why are stable molecules (H2) forming ions when its wrote in my guides that substances ionise to become more stable. Are H+ ions-that dont have a full outer shell- more stable than covalently bonded H-H molecules which have a full outer shell?
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Kian Stevens
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(Original post by SoorajG1)
Okay but, why are stable molecules (H2) forming ions when its wrote in my guides that substances ionise to become more stable. Are H+ ions-that dont have a full outer shell- more stable than covalently bonded H-H molecules which have a full outer shell?
You don't need to know how the oxidation occurs, you just need to know that it does.
But in essence, the dihydrogen molecules attach to a membrane, which catalyses the oxidation of them.

Only some things will spontaneously ionise to become more stable, such as the group 1 metals. Some things will do the opposite to become more stable, such as the halogens, which reduce. In general, things do this to acquire the same electronic configuration as the nearest noble gas; these are inert, meaning they're very stable.
However, dihydrogen is a perfectly stable molecule at RTP, and this is why the membrane is required, to assist in its oxidation. It won't just spontaneously oxidise, as this is an unfavourable process in terms of thermodynamics.

H+ ions don't have an outer shell at all, as their 1s orbital has been lost; they simply have no electron density.
H+ ions are literally just bare protons, and these are nowhere near as stable as a dihydrogen molecule, hence why the spontaneous oxidation of dihydrogen molecules is thermodynamically unfavourable.
Last edited by Kian Stevens; 3 years ago
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