Q.

Standard electrode potentials for a few half cells are mentioned below:

ECu2+/Cu=0.34 V,   EZn2+/Zn=-0.76 V

EAg+/Ag=0.80 V,  EMg2+/Mg=-2.37 V

Which one of the following cells gives the most negative value of ΔG°         [2025]

1 ZnZn2+(1M)Ag+(1M)Ag  
2 CuCu2+(1M)Ag+(1M)Ag  
3 ZnZn2+(1M)Mg2+(1M)Mg  
4 AgAg+(1M)Mg2+(1M)Mg  

Ans.

(1)

Cell Representation Ecell=Ecathode-Eanode ΔGcell=-nFEcell
Zn|Zn2+(1M)Ag+(1M)|Ag Ecell=EAg+/Ag-EZn2+/Zn=[0.80-(-0.76)]V=1.56 V ΔGcell=-2F×1.56=-3.12F
Cu|Cu2+(1M)Ag+(1M)|Ag Ecell=EAg+/Ag-ECu2+/Cu=[0.80-0.34]V=0.46 V ΔGcell=-2F×0.46=-0.92F
Zn|Zn2+(1M)Mg2+(1M)|Ag Ecell=EMg2+/Mg-EZn2+/Zn=[-2.37-(-0.76)]V=-1.61 V ΔGcell=-2F×(-1.61)=3.22F
Ag|Ag+(1M)Mg2+(1M)|Mg Ecell=EMg2+/Mg-EAg+/Ag=[-2.37-0.80]V=-3.17 V ΔGcell=-2F×(-3.17)=6.34F