When should I use 0.0257 or 0.0592?

Question

There are two equations:

E= E° = (0.0257/n)(ln(Q)) and E= E° = (0.0592/n)(log(Q)).

When should I use 0.0257? When should I use 0.0592?

Answer 1

The full Nernst equation is E = E₀ + (RT/nF)lnQ The R should be 8.314 J/mole K and T is taken as 298.15K and the Faraday constant is 96,485 Coulombs/mole of electrons. That leads to

the term (.02569/n_e) lnQ is obtained. So your first equation is correct for 25°C

the second equation is also correct with log meaning log base 10 (again, limited to 25°C)

ln(x) = log(x)/log(e) which obtains the .05915 coefficient.