Ncert Exercises & Solutions

8.4: The $E^{θ} (M^{2 +} / M)$ value for copper is positive (+0.34V). What is possibly the reason for this? (Hint: consider its high

$∆ a H^{θ} a n d l o w ∆_{h y d} H^{θ})$

The

E^{θ} (M^{2 +} / M)

value of a metal depends on the energy changes involved in the following:

1. Sublimation: The energy required for converting one mole of an atom from the solid state to the gaseous state.

M_{(s)} \to M_{(g)}

∆_{s} H

(Sublimation energy)

2. Ionization: The energy required to take out electrons from one mole of atoms in the gaseous state.

M_{(s)} \to M_{(g)}

∆_{i} H

(Ionization energy)

3. Hydration: The energy released when one mole of ions are hydrated.

M^{2 +} \to {M^{2 +}}_{(a q)} ∆_{h y d} H

(Hydration energy)

Now, copper has a high energy of atomization and low hydration energy. Hence, the

E^{θ} (M^{2 +} / M)

value for copper is positive.