The $E^{\theta}\left(\mathrm{M}^{2+} / \mathrm{M}\right)$ value for copper is positive $(+0.34 \mathrm{~V})$. What is possibly the reason for this? (Hint: consider its high $\Delta_{\mathrm{a}} H^{\theta}$ and low $\Delta_{\text {hyd }} H^{\theta}$ )
The Eθ(M2+/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.
$\mathrm{M}_{(s)} \longrightarrow \mathrm{M}_{(g)} \quad \Delta_{\mathrm{s}} H$ (Sublimation energy)
2. Ionization: The energy required to take out electrons from one mole of atoms in the gaseous state.
$\mathrm{M}_{(g)} \longrightarrow \mathrm{M}^{2+}{ }_{(g)} \quad \Delta_{\mathrm{i}} H$ (Ionization energy)
3. Hydration: The energy released when one mole of ions are hydrated.
$\mathrm{M}^{2+}{ }_{(g)} \longrightarrow \mathrm{M}^{2+}{ }_{(a q)} \quad \Delta_{\text {liyd }} H($ Hydration energy $)$
Now, copper has a high energy of atomization and low hydration energy. Hence, the Eθ(M2+/M) value for copper is positive.
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