Which transition metal of 3d series has positive E° (M2+/M) value and why?
Solution
Copper is the transition metal of 3d series that exhibits positive E0(M2+/M). The value of E0(M2+/M) for copper is (+0.34). This happens because the E0(M2+/M) value of a metal depends on the energy changes involved in the following:
1. Sublimation energy: The energy required for converting one mole of an atom from the solid state to the gaseous state.
M(s)→→ M(g) ΔsH (Sublimation energy)
2. Ionisation energy: The energy required to take out electrons from one mole of atom in the isolated gaseous state.
M(g) →→ M2+(g) ΔiH (Ionisation energy)
3. Hydration energy: The energy released when one mole of ions are hydrated.
M2+(g) →→M2+(aq) ΔhydH (Hydration energy)
Since, copper has a high energy of atomisation and low hydration energy, the E0(M2+/M) value for copper is positive.
