Q.

For the electro chemical cell

M|M2+X|X2-

If E(M2+/M)=0.46V and E(X/X2-)=0.34V.

Which of the following is correct                                     [2024]

1 Ecell=0.80V  
2 M+XM2++X2- is a spontaneous reaction  
3 Ecell=-0.80V  
4 M2++X2-M+X is a spontaneous reaction  

Ans.

(4)

               Anode half cell reaction:

               MM2++2e-, EM2+/M=0.46V

               Cathode half cell reaction:

               X+2e-X2-, EX/X2-=0.34V

               Net reaction:

               M+XM2++X2-,

              Ereaction=EX/X2--EM2+/M

                             =(0.34-0.46)V=-0.12V

            As potential for the reaction M+XM2++X2- is negative, this reaction is non spontaneous.

            So its reverse reaction i.e. M2++X2-M+X is spontaneous.