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Question #44900

Difficulty: 8/10 | 🟢 Free

The Question

An electrochemical cell operates at 1000 K1000\text{ K} in an inert molten fluorocarbon solvent. The cathode compartment contains a mixture of solid \ceMF4\ce{MF_4} and \ceMF3\ce{MF_3}, while the anode is a standard fluorine gas electrode (12\ceF2(g)+e−→\ceF−(melt)\frac{1}{2} \ce{F2(g)} + e^- \rightarrow \ce{F^- (melt)}, E∘=0.00 VE^\circ = 0.00\text{ V}). \ \ Given the following standard thermodynamic data at 1000 K1000\text{ K}:\ ∙\bullet ΔGsublimation∘(M)=500 kJ/mol\Delta G^\circ_{\text{sublimation}}(M) = 500\text{ kJ/mol}\ ∙\bullet ∑i=13IEi(M)=4000 kJ/mol\sum_{i=1}^{3} IE_i(M) = 4000\text{ kJ/mol}\ ∙\bullet IE4(M)=4767 kJ/molIE_4(M) = 4767\text{ kJ/mol}\ ∙\bullet ΔGdissociation∘(\ceF2)=160 kJ/mol\Delta G^\circ_{\text{dissociation}}(\ce{F2}) = 160\text{ kJ/mol}\ ∙\bullet ΔGelectron affinity∘(\ceF)=−340 kJ/mol\Delta G^\circ_{\text{electron affinity}}(\ce{F}) = -340\text{ kJ/mol}\ ∙\bullet ΔGlattice∘(\ceMF3)=−5500 kJ/mol\Delta G^\circ_{\text{lattice}}(\ce{MF_3}) = -5500\text{ kJ/mol}\ ∙\bullet ΔGlattice∘(\ceMF4)=−10200 kJ/mol\Delta G^\circ_{\text{lattice}}(\ce{MF_4}) = -10200\text{ kJ/mol}\ ∙\bullet ΔGsolvation∘(\ceF−,melt)=−400 kJ/mol\Delta G^\circ_{\text{solvation}}(\ce{F^-}, \text{melt}) = -400\text{ kJ/mol}\ \ Calculate the standard reduction potential (E∘E^\circ) for the half-cell reaction: \ \ceMF4(s)+e−−>MF3(s)+F−(melt)\ce{MF_4(s) + e^- -> MF_3(s) + F^- (melt)}\ \ (Assume Faraday's constant F=96500 C/molF = 96500\text{ C/mol})

Options

  • A.

    −2.00 V-2.00\text{ V}

  • B.

    +2.00 V+2.00\text{ V}

  • C.

    +0.69 V+0.69\text{ V}

  • D.

    +4.84 V+4.84\text{ V}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

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Concepts Behind This Question

Stability of High O.S. Fluorides/Oxides|Gibbs Energy and Spontaneity|Electrolysis Product Prediction

Why This Question Is Tricky

Common Mistakes

This problem tests the thermodynamic stability of high oxidation states stabilized by fluorine's immense lattice energy.

The primary trap is the 'Hidden Variable' of the reference electrode: students often attempt to calculate the absolute half-cell potential by erroneously incorporating the solvation energy of the fluoride ion in the melt.

However, when referenced against the standard fluorine electrode in the same medium, the solvated fluoride ion cancels out of the overall cell equation.

Furthermore, it highlights that despite a massive 4th ionization energy, the +4+4 state is thermodynamically stable against reduction due to the highly exothermic lattice energy of MF4, resulting in a negative reduction potential.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterD and F Block Elements - Class 12
ConceptStability of High O.S. Fluorides/Oxides
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree