Reversing Potentials

[Ellen Amico 2L]

How do we know when we need to reverse a reduction equation (to make it oxidation) and therefore multiply the reduction potential by -1?

[Deepika Reddy 1A]

After looking at both reduction potentials, you reverse the one that has a lower reduction potential. This is because the one with the higher reduction potential is more likely to be reduced than the one with the lower reduction potential. So, therefore, you reverse the one with the lower reduction potential as it will get oxidized instead.

[Norman Dis4C]

Honestly, it would not matter. If your E is negative, you simply reverse it and the position of reactants and products.

[Susanna Givan 2B]

You just are trying to cancel out the charges typically, so manipulate the equations to reflect that.

[kareena_prasad]

You can tell by the redox equation. The process of determining the sign of E is similar to determining the sign of enthalpy in thermochemistry, but the difference is that in thermochemistry you would multiply enthalpy by a constant if you were increasing the amount of moles, which you do not do in electrochemistry because E˚ is an intensive property.

[joshua_quinn_1C]

Since E must be positive for the two half reactions, you would take the half reaction with the lowest E and reverse that to get the redox reaction since that would lead to the most positive E value. Hope this helps!

[Rena Wu 3E]

Hi Ellen, you would typically reverse reduction equations depending on the redox equation as a whole. Looking at which molecule/atom is losing electrons (being oxidized) can help to determine which reduction reaction must be reversed. You can usually also see the charges/electrons in both half-reactions and manipulate the two equations from there. Hope this helps!

[LouiseLin2L]

After balancing your reactions and write out the appropriate half reactions, I think you just find out which E, after you flip the sign, would still bring us to a positive overall E after adding to the other half E.