(i) Why is E^0 Cu^2+ ICu value exceptionally positive?

Question

From the given data of E⁰ values answer the following:

Element	Cr	Mn	Fe	Co	Ni	Cu
E0Mn2+1Mn	0.091	-1.18	-0.44	-0.28	-0.25	+0.34

(i) Why is E⁰ Cu²⁺ ICu value exceptionally positive? 

(ii) Why is E⁰Mn²⁺ I Mn value highly negative as compared to other elements ? 

(iii) Which is a stronger reducing agent Cr²⁺ or Fe²⁺?

Answer 1

(i) Electrode potential value is the sum of three factors, enthalpy of atomisation, ionisation enthalpy and hydration enthalpy. In case of copper the sum of enthalpy of atomisation and ionisation enthalpy is higher than hydration enthalpy. 

Therefore E⁰ Cu²⁺ I Cu value is exceptionally positive. 

(ii) Mn²⁺ has stable electronic configuration (3d⁵). The ionisation enthalpy is less than that of hydration enthalpy. Therefore E⁰ value is more negative. 

(iii) Cr²⁺ is stronger reducing agent than Fe²⁺ due to more negative E⁰ value