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Question #44773

Difficulty: 8/10 | 🟢 Free

The Question

A \ce{H2-O2} fuel cell operates using an aqueous \ce{KOH} electrolyte. Due to continuous operation and solvent evaporation, the boiling point of the electrolyte solution is elevated by 0.0104 K0.0104 \text{ K}. Assume the density of the dilute solution is 1.0 kg L−11.0 \text{ kg L}^{-1} (molarity ≈\approx molality). The standard reversible potential of the cell is E∘=1.23 VE^\circ = 1.23 \text{ V}. The cell operates at a constant current of I=46 mAI = 46 \text{ mA} and has a cell constant G∗=0.01 cm−1G^* = 0.01 \text{ cm}^{-1}. The molar conductivity of the \ce{KOH} solution follows the Debye-Hückel-Onsager equation: Λm=Λm∘−BC\Lambda_m = \Lambda_m^\circ - B\sqrt{C}. Given: Kb(\ceH2O)=0.52 K kg mol−1K_b(\ce{H2O}) = 0.52 \text{ K kg mol}^{-1}, Λm∘=250 S cm2 mol−1\Lambda_m^\circ = 250 \text{ S cm}^2 \text{ mol}^{-1}, B=500 S cm2 mol−3/2 L1/2B = 500 \text{ S cm}^2 \text{ mol}^{-3/2} \text{ L}^{1/2}. Assuming activation and concentration overpotentials are negligible, what is the operational voltage (VcellV_{cell}) of the fuel cell at this state?

Options

  • A.

    1.00 V1.00 \text{ V}

  • B.

    1.10 V1.10 \text{ V}

  • C.

    1.05 V1.05 \text{ V}

  • D.

    1.46 V1.46 \text{ V}

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Numerical_Precision

Improve calculation stamina and avoid rounding errors in high-stakes competitive examinations.

Concepts Behind This Question

Fuel Cell Efficiency|Molar Conductivity Trend|Boiling Point Elevation (Solvent vs Solution)

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of Colligative Properties, Conductance, and Fuel Cell Thermodynamics.

Students often treat fuel cell electrolytes as ideal, constant resistors.

The primary trap is forgetting the van 't Hoff factor (i=2i=2) for the strong electrolyte \ce{KOH} during the boiling point elevation step.

If i=1i=1 is mistakenly used, the calculated concentration doubles (0.02 M0.02 \text{ M}), leading to an incorrect molar conductivity (≈179.3 S cm2 mol−1\approx 179.3 \text{ S cm}^2 \text{ mol}^{-1}), an incorrect internal resistance, and ultimately the distractor 1.10 V1.10 \text{ V}.

A secondary trap involves ignoring the Debye-Hückel-Onsager non-ideal behavior entirely and using Λm∘\Lambda_m^\circ, which leads to 1.05 V1.05 \text{ V}.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterElectrochemistry - Class 12
ConceptFuel Cell Efficiency
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree