E cell value

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Chew 2H
Posts: 34
Joined: Fri Sep 29, 2017 7:05 am

E cell value

Postby Chew 2H » Wed Mar 14, 2018 2:34 pm

In the second electrochem problem Lavelle went through today in lecture, why did we flip the E value for the second equation? Do we always flip the equation with a much more negative value?

Ashley Davis 1I
Posts: 57
Joined: Fri Sep 29, 2017 7:04 am

Re: E cell value

Postby Ashley Davis 1I » Wed Mar 14, 2018 2:40 pm

So because this is a Galvanic cell, we know that we want our Eº(cell) to be positive. We know that we're going to have to reverse one of the reduction half-reactions so that we have one reduction and one oxidation. Since our Eº(cell) needs to be positive, we'll need to make the larger of the two standard potentials positive. Then when we combine the half-reactions, adding the two standard potentials together gives us a positive Eº(cell).

Basically we flipped the second reaction because making its standard potential positive would give us a positive Eº(cell).

Chew 2H
Posts: 34
Joined: Fri Sep 29, 2017 7:05 am

Re: E cell value

Postby Chew 2H » Wed Mar 14, 2018 2:54 pm

Thank you! And if it wasn't a galvanic cell, and the overall E could be negative. how do we know which one to flip?


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