Question

Assertion (A): $E^\circ_{Cu^{2+}/Cu} = +0.34$ V.
Reason (R): It is due to low $\Delta H^\circ_{hyd}$ and high $\Delta H^\circ_a$.

• A. Both A and R are true and R is the correct explanation of A.
• B. Both A and R are true but R is not the correct explanation of A.
• C. A is true but R is false.
• D. A is false but R is true.

Hint:

Cu has positive $E^\circ$ because high $\Delta H^\circ_a$ and $\Delta H^\circ_{IE}$ are not compensated by (insufficient) $\Delta H^\circ_{hyd}$.

Answer 1

The Correct Option is C

Step 1: Concept
The standard electrode potential of a metal depends on the net thermodynamic balance of sublimation enthalpy ($\Delta H^\circ_a$), ionization enthalpy ($\Delta H^\circ_{IE}$), and hydration enthalpy ($\Delta H^\circ_{hyd}$).

Step 2: Analysis
The Assertion is true: copper has a positive $E^\circ$ of $+0.34$ V. The Reason is false: the positive $E^\circ$ of Cu is due to its high atomization enthalpy ($\Delta H^\circ_a$) and high ionization enthalpy, which are NOT compensated by the relatively low hydration enthalpy. Therefore, the net energy cost of dissolving Cu as $Cu^{2+}$ is large, making the reduction favorable (positive $E^\circ$). The Reason states the direction of $\Delta H^\circ_{hyd}$ incorrectly.

Step 3: Conclusion
The Assertion is correct, but the Reason incorrectly describes the thermodynamic relationship.

Final Answer: (C)