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Question #44739

Difficulty: 8/10 | 🟢 Free

The Question

The standard reduction potentials ( $E^\circ$ ) for the $\ce{MCl6^{2-}}/\ce{MCl4^{2-}}$ redox couples of Palladium (Pd, 4d) and Platinum (Pt, 5d) at 298 K differ by $0.61 \text{ V}$ .

An aqueous solution is prepared by mixing equimolar amounts of $\ce{K2PdCl4}$ , $\ce{K2PtCl4}$ , $\ce{K2PdCl6}$ , and $\ce{K2PtCl6}$ at 298 K. A spontaneous redox reaction occurs.

Based on the anomalous stability of higher oxidation states in 5d elements relative to 4d elements (a consequence of the lanthanoid contraction), determine the standard Gibbs free energy change ( $\Delta G^\circ$ ) for the spontaneous reaction, and the number of $d$ -electrons present in the central metal ion of the product complex containing the 5d element. (Given: $F = 96500 \text{ C/mol}$ . Assume no side reactions occur.)

Options

A.
-117.73 kJ/mol, 6
B.
-117.73 kJ/mol, 8
C.
-58.86 kJ/mol, 6
D.
-58.86 kJ/mol, 8

Check Your Answer

Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Gibbs Energy and Spontaneity|Variable Oxidation State Stability|Post-Lanthanoid Radii Equality|d-orbital contraction

Why This Question Is Tricky

Common Mistakes

Students often incorrectly apply p-block periodic trends (like the inert pair effect) to d-block elements, assuming higher oxidation states become less stable down a group.

However, in transition metals, higher oxidation states become MORE stable down a group.

Specifically, the 5d element Pt(IV) is more stable than the 4d element Pd(IV) due to the lanthanoid contraction.

Students failing to recognize this will reverse the spontaneous reaction, incorrectly identifying Pt(II) as the product and miscalculating the d-electron count as 8 instead of 6.

Furthermore, students might use n=1 instead of n=2 for the two-electron transfer, leading to an incorrect $\Delta G^\circ$ .

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Electrochemistry - Class 12
Concept	Gibbs Energy and Spontaneity
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free