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swapping signs of E values

Posted: Thu Feb 22, 2018 7:30 pm
When we are trying to find the Ecell how do we know which one of the two equations we swap the sign of?

Re: swapping signs of E values

Posted: Thu Feb 22, 2018 7:41 pm
If you use the formula $E_{cell}^{\circ} = E_{cathode}^{\circ} - E_{anode}^{\circ}$ you do not need to change the sign of $E^{\circ}$ for either half reaction because the minus sign does it for you.

Re: swapping signs of E values

Posted: Sun Feb 25, 2018 2:10 pm
You can also use the equation $E=E_{oxidation}+E_{reduction}$

Re: swapping signs of E values

Posted: Sun Feb 25, 2018 2:36 pm
I think Dr. Lavelle prefers that we use:
Eocell = Eocathode - Eoanode
so that we don't have to switch the sign of either standard reduction potential

Re: swapping signs of E values

Posted: Sun Feb 25, 2018 3:47 pm
The main thing you have to remember when you use the Cathode-Anode equation is that both the Enaught values that you use have to be reduction half reaction potential values.

Re: swapping signs of E values

Posted: Sun Feb 25, 2018 4:16 pm
I use Eo(cell) = Eo(cathode) - Eo(anode) so that way I do not need to flip any signs.

Re: swapping signs of E values

Posted: Sun Feb 25, 2018 8:24 pm
You usually swap the sign of the equation that needs to be oxidized. Since the back of the book only lists reduction potentials, and a redox reaction has both reduction and oxidation half reactions, we need to flip one of the equations to turn it into an oxidation. Turning a half reaction from a reduction to an oxidation basically means you are reversing the equation, in which case you need to change the sign of E naught.

Re: swapping signs of E values

Posted: Sun Feb 25, 2018 8:30 pm
Yeah I also do what Ridhi does which is flipping the sign of the oxidation reaction since the appendix contains the reduction potentials. Either way works though, it all just depends on what way works best for you.

Re: swapping signs of E values

Posted: Mon Feb 26, 2018 9:20 pm
You swipe the sign on the anode by using the equation Ecell=Ecathode-Eanode