Electrolysis: Water 1/2 Rxn

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Sydney Wu 2M
Posts: 50
Joined: Fri Jul 22, 2016 3:00 am

Electrolysis: Water 1/2 Rxn

Postby Sydney Wu 2M » Fri Feb 10, 2017 6:16 am

The textbook gives us:

2 H2(g) + O2(g) --> 2 H2O(l) Ecell = +1.23V at pH = 7
2 H2O(l) --> 2 H2(g) + O2(g) Ecell = -1.23V at pH = 7
O2(g) + 4 H+ (aq) + 4e- --> 2 H2O(l) E = +0.82V at pH = 7

How do we know when to use these equations as an anode or cathode reaction, and how do we determine which one to use?

Ara Yazaryan 1E
Posts: 44
Joined: Wed Sep 21, 2016 2:59 pm

Re: Electrolysis: Water 1/2 Rxn

Postby Ara Yazaryan 1E » Fri Feb 10, 2017 8:07 pm

Well the first to you gave are the same reaction, except one is the oxidation and the other is the reduction reaction. As for the third reaction, that is for the formation of water from diatomic hydrogen and oxygen. Thus the question would have to explicitly state "water is formed from hydrogen and oxygen gas" so it would be relatively clear when to use this equation.

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