The `E^(Theta) (M^(2+)//M)` value for copper is positive `(+0.34V)`. What is possibly the reason for this? (Hint: consider its high `Delta_(a)H^(Theta)` and low `Delta_("hyd")H^(Theta)` )

Explanation

`E^(@)(M^(2+)//M)` value for any metal depends on three factors :
i) `Delta_(a)H` (Enthalpy of atomisation), `M(s)+ Delta_(a)H rarr M(g)`
ii) `Delta_(i)H` (Enthalpy of ionisation), `M(g)+Delta_(i)H rarr M^(2+)(g)`
iii) `Delta_(hyd)H` (Hydration enthalpy), `M^(2+)(g)+(aq rarr M^(2+) (aq)`
Copper has high value of enthalpy of atomisation and low value of enthalpy of hydration. It means that `Delta_(i)H` required is not compensated by the energy released. Therefore, `E_((Cu^(2+)//Cu))^(0)` is positive.