changing half reactions

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Jorja De Jesus 2C
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changing half reactions

Postby Jorja De Jesus 2C » Sat Mar 14, 2020 8:45 pm

When the half reactions are both reduction reactions or both oxidization reactions you change one of them by switching them around and changing the sign of the cell potentials right? How do you know which one to change so that they are no longer the same?

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Re: changing half reactions

Postby vpena_1I » Sat Mar 14, 2020 9:03 pm

you flip whichever one would give you the most positive delta E*cell

Ashley Wang 4G
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Re: changing half reactions

Postby Ashley Wang 4G » Sat Mar 14, 2020 10:45 pm

They'll most likely both be given with an associated standard reduction potential (Eº), so you'll identify the half-reaction with the more positive Eº as the reduction half reaction, and the other when (when flipped) will be the oxidation half reaction.

Bryce Ramirez 1J
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Re: changing half reactions

Postby Bryce Ramirez 1J » Sat Mar 14, 2020 11:14 pm

To find which one is the oxidation half and which one is the reduction half, you subtract the two Ecells and whichever one gives you a positive Ecell is the correct order. Then you analyze which numbers are in which position. The one on the left is the cathode and the one on the right is the anode.

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Re: changing half reactions

Postby gconcha » Sun Mar 15, 2020 4:53 am

You want the cell to transfer electrons from anode to cathode, from negative to positive (it's for this reason that the anode is always on the left and the cathode is always on the right). In order to do that, you usually want the potential difference to be positive. Therefore, the one with the greater magnitude (larger number) is the one that you want as your cathode. That's the one you flip.

Rafsan Rana 1A
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Re: changing half reactions

Postby Rafsan Rana 1A » Sun Mar 15, 2020 3:35 pm

In the anode, usually the reverse of the given half reactions is occuring, because oxidation has to take place in the anode, right?

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Re: changing half reactions

Postby Mulin_Li_2J » Sun Mar 15, 2020 4:12 pm

Depends on what you want. By default, all the half-rxns should be presented in reduction formats. If you are trying to calculate E, flip the one with lower E and then simply add two cell potential together. Or instead of flipping any of the two, you can minus the lower half-rxn cell potential from the higher half-rxn cell potential. Either way works.

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