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Question #44233

Difficulty: 8/10 | 🟢 Free

The Question

A closed reaction vessel at 298 K298 \text{ K} contains a standard acidic aqueous solution ([\ceH+]=1.0 M[\ce{H^+}] = 1.0 \text{ M}). To this, 1.0 mole1.0 \text{ mole} of \ceKMnO4\ce{KMnO4} and 4.0 moles4.0 \text{ moles} of \ceMnSO4\ce{MnSO4} are added. The system is allowed to reach complete thermodynamic equilibrium.

Given the standard reduction potentials at 298 K298 \text{ K}: E∘(\ceMnO4−/Mn2+)=+1.51 VE^\circ(\ce{MnO4^- / Mn^{2+}}) = +1.51 \text{ V} E∘(\ceMnO2/Mn2+)=+1.23 VE^\circ(\ce{MnO2 / Mn^{2+}}) = +1.23 \text{ V} E∘(\ceMn3+/Mn2+)=+1.51 VE^\circ(\ce{Mn^{3+} / Mn^{2+}}) = +1.51 \text{ V}

Calculate the total standard Gibbs free energy change (ΔGtotal∘\Delta G^\circ_{total}) for the complete conversion of the given amounts of reactants to their most thermodynamically stable products. (Assume ideal behavior, standard states for all species except the initial stoichiometric amounts provided, and F=96500 C mol−1F = 96500 \text{ C mol}^{-1})

Options

  • A.

    0.0 kJ0.0 \text{ kJ}

  • B.

    −135.1 kJ-135.1 \text{ kJ}

  • C.

    −270.2 kJ-270.2 \text{ kJ}

  • D.

    −54.0 kJ-54.0 \text{ kJ}

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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

Hess's Law Application|Comproportionation Reversibility|Oxidation State Extremes

Why This Question Is Tricky

Common Mistakes

The problem tests the distinction between a stoichiometric intermediate state and the true thermodynamic ground state.

The 1:4 reactant ratio perfectly baits students into calculating the ΔG∘\Delta G^\circ for the comproportionation to \ceMn3+\ce{Mn^{3+}}, which yields exactly 0.0 kJ0.0 \text{ kJ}.

The hidden variable is the thermodynamic instability (metastability) of \ceMn3+\ce{Mn^{3+}} in aqueous acidic medium, which disproportionates into \ceMnO2\ce{MnO2} and \ceMn2+\ce{Mn^{2+}}.

Students must apply Hess's Law (or Frost diagram analysis) to bypass the metastable intermediate and calculate the free energy change for the complete resolution to the thermodynamically stable products.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterThermodynamics - Class 11 Part 1
ConceptHess's Law Application
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree