I have a question about voltages including redox reactions. I know that half equations may have negative voltages when choosing what is undergoing reduction, and what is undergoing oxidation in a chemical reaction, but can a whole redox reaction have a negative voltage?

Say, a potential of

$$\ce{A+ + B -> B+ + A}$$

is equal to $2.5~\mathrm V$. Surely this does not mean that the reaction occurs the other way either?

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    $\begingroup$ A spontaneous redox reaction will always have a positive E cell by current conventions of electrochemistry. A whole redox reaction can have negative potential if you have switched the anode and the cathode. All it physically means is that your chosen cathode is actually an anode and vice versa. $\endgroup$ – M. Farooq May 6 '19 at 11:15

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