1)
DrG = – 2FE(cell)
but when we write the reaction
2 Zn (s) + 2 Cu2+(aq) ¾®2 Zn2+(aq) + 2Cu(s)
DrG = – 4FE(cell)
If the concentration of all the reacting species is unity, then
E(cell) = 
(
)
o
Ecell
 and we have
DrGo = – nF
o
E(cell)
(2 16)
Thus, from the measurement of 
(
)
o
Ecell
 we can obtain an important
thermodynamic quantity, DrGo, standard Gibbs energy of the reaction From the latter we can calculate equilibrium constant by the equation:
DrGo = –RT ln K 2