Question

What is the relationship between Gibbs free enrgy of the cell reaction in a galvanic cell and the emf of the cell? When will the maximum work be obtained from a galvanic cell? When will the maximum work be obtained from a galvanic cell?

Answer 1

If concentration of all reacting species is unity, then `E_("cell")=E_("Cell")^(@)` and `DeltaG^(@)=-nFE_("cell")^(@)`
where, `DeltaG_(r)G^(@)` is stan dard Gibbs energy of the reaction
`E_("cell")^(@)=` emf of the cell
`nF=`charge passed
If we want to obtain m aximum work from a galvanic cell then charge has to be passed reversible.
The reversibly work done by a galvanic cell is equal to decrease in its Gibbs energy
`Delta_(r)G=-nFE_("cell")`
As `E_("cell")` is an intensive parameter but `Delta_(f)=G` is an extensive thermodynamic property and the value depends on n.
For reaction, `Zn(s)+Cu^(2+)(aq)rarrZn^(2+)(aq)+Cu(s)` in a galvanic cell.
`Delta_(r)G=-2FE_("cell")` [Here,n=2]