Explain with reference to the Nernst equation, how is it possible for a cell to have a positive cell potential understandard conditions but the negative cell potential under other conditions.
The Nernst equation is
Ecell = Eocell + (0.05916/n)*log(reduced/oxidized)
As the concn changes, the reduced form and oxidized form changes, that changes the log and adds or subtracts from Eocell. By adding and/or subtracting from Eocell with concn, it is possible to make the cell "go the other direction," meaning it changes sign.