Cell potential calculation

[Aijun Zhang 1D]

Just a quick question.
When we calculate cell potential for a reaction composed of two half reactions. Do we always subtract the smaller standard reduction potential from the larger one? Therefore the final result is always positive?

Thank you!

[Wenjie Dong 2E]

I guess you should always reverse the less reactive one.

[Anna Li 2E]

Galvanic cells generate electrical energy from spontaneous redox reactions, meaning that the deltaG (gibb's free energy) should be negative as we know that indicates spontaneous reactions. When reactions are spontaneous that means that E MUST be positive. So when you are adding/subtracting cell potentials, you should reverse the E value that keeps the total E as a positive number.

[Nathan Tu 2C]

If the cell is not a galvanic cell, or rather the case in any cell, subtract the E anode from E cathode which means subtracting the E of the oxidation reaction from the E of the reduction reaction. If the answer is not positive, than the cell is not a galvanic cell.

[Ya Gao]

There are two ways to calculate the cell potential. 1st: list out the anode and cathode reaction and copy the corresponding cell potential to these two reaction. Cell potential of this reaction equals to cell potential of the cathode reaction minus the cell potential of the anode reaction.

2nd: list out the anode and cathode reaction and reverse the anode reaction and therefore, the cell potential for the anode reaction has to be reversed as well. Cell potential of this reaction equals to cell potential of the cathode adds the cell potential of the anode.