Reduction Half-Reactions

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Justin Chu 1G
Posts: 52
Joined: Thu Jul 13, 2017 3:00 am
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Reduction Half-Reactions

Postby Justin Chu 1G » Wed Feb 21, 2018 5:36 pm

How come when using the equation E(cathode)-E(anode), you don't flip the sign of the reduction potential if you are reversing the equation?

Ava Harvey 2B
Posts: 54
Joined: Fri Sep 29, 2017 7:04 am

Re: Reduction Half-Reactions

Postby Ava Harvey 2B » Wed Feb 21, 2018 7:29 pm

I was a bit confused on this concept as well, but Lavelle mentioned two different methods in lecture for solving for the standard cell potential. So all of the half-reactions are given in the reduction form, and thus so are the corresponding standard potentials. Once you have determined which half-reaction is being reduced (cathode) and which is being oxidized (anode), as well as found their corresponding standard potentials, reverse the sign for the half-reaction that is being oxidized (anode). Once you have done that, all you need to do is add those two standard potentials together to get the final standard cell potential (it doesn't matter which one you add first). Instead of using the equation E(cell) = E(cathode) - E(anode), I think this way is a bit easier. It's basically the same exact concept, it's just thinking about it in a different way. For me, it also helps to ensure that I am not messing up a sign. Hope this helps!

Tiffany 1B
Posts: 32
Joined: Fri Sep 29, 2017 7:05 am

Re: Reduction Half-Reactions

Postby Tiffany 1B » Wed Feb 21, 2018 8:18 pm

So I believe this is because the equation itself accounts for the sign change, but as Ava said you can change the sign and then simply add them (instead of subtracting them). Hope that helps.

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