`E^(@)` of Cu is + 0.34 V while that of Zn is – 0.76 V. Explain.

Explanation

High ionisation enthalpy to change Cu (s) to `Cu^(2+)` is not balanced by hydration enthalpy. Therefore, it exhibits a positive `E^(@)` value. However, Zn exhibits a lower value of ionization enthalpy because a stable `3d^(10)` configuration is attained after losing two electrons. The hydration energy for `Zn^(2+)` is comparable to that of `Cu^(2+)`. Therefore, `Eo^(@)` for Zn is negative.