Question

Ni-cad (nickel–cadmium) batteries have a slightly lower cell potential than the common alkaline value of 1.5 v normally used in flashlights. they have a cadmium anode, which is oxidized to cd(oh)2(s) in a basic background electrolyte of concentrated oh–, and a cathode half-reaction in which nio(oh)(s) is reduced to ni(oh)2(s). what is the value of δg°cell?

Answer 1

The half-reaction are:

Cd ---> Cd(OH)₂
The oxidation number of Cd changed from 0 to +2. So, the number of mol electron transferred here is 2.

NiO(OH) --> Ni(OH)₂
The oxidation number of Cd changed from +3 to +2. So, the number of mol electron transferred here is 1.

Now, the greatest common factor would be 2. So, we use n=2 for the formula for ΔG°. F is Faraday's constant equal to 96,485 J/mol e.

ΔG° = nFE° = (2)(96,485)(1.5) = 289,455 J