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Question #44772

Difficulty: 8/10 | 🟢 Free

The Question

A modified \ce{H2-O2} fuel cell operates at 298 K298 \text{ K} using a dual-membrane system that creates an internal concentration gradient. The anode compartment interfaces with a weak polymeric acid membrane (effective monomeric concentration C=0.1 MC = 0.1 \text{ M}, acid dissociation constant Ka=10−5K_a = 10^{-5}). The cathode compartment interfaces with a fully dissociated strong acid membrane (C=0.1 MC = 0.1 \text{ M}). Both \ce{H2} and \ce{O2} gases are supplied at 1 bar1 \text{ bar}. Given the standard cell potential E∘=1.23 VE^\circ = 1.23 \text{ V}, the standard enthalpy of combustion of \ce{H2(g)} to \ce{H2O(l)} as ΔH∘=−289.5 kJ/mol\Delta H^\circ = -289.5 \text{ kJ/mol}, and Faraday's constant F=96500 C/molF = 96500 \text{ C/mol}. Assuming 2.303RTF=0.059 V\frac{2.303 RT}{F} = 0.059 \text{ V} at 298 K298 \text{ K}, what is the theoretical thermodynamic efficiency (η=ΔGΔH×100\eta = \frac{\Delta G}{\Delta H} \times 100) of this modified fuel cell?

Options

  • A.

    89.87%

  • B.

    82.00%

  • C.

    85.93%

  • D.

    74.13%

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Mechanism_Trap

Don't get tricked by the process! Learn the mechanical traps used in competitive exam questions.

Concepts Behind This Question

Fuel Cell Efficiency|Concentration Cells|Degree of Dissociation (Alpha)

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of electrochemistry (fuel cells/concentration cells) and ionic equilibrium.

The 'Hidden Variable' is the degree of dissociation (α\alpha) of the weak acid membrane.

Students often blindly plug the analytical concentration (0.1 M0.1 \text{ M}) into the Nernst equation, assuming ideal behavior or full dissociation (α=1\alpha = 1), which leads to an incorrect EcellE_{cell} of 1.23 V1.23 \text{ V} and an efficiency of 82.00%82.00\%.

By forcing the calculation of actual proton activity (a=αCa = \alpha C), the problem highlights the thermodynamic reality of polymer electrolyte membranes where partial dissociation dictates the effective charge carrier concentration.

Quick Facts About This Question

Question Information

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