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Question #44765

Difficulty: 8/10 | 🟢 Free

The Question

A lead storage battery operates at 298 K298 \text{ K} with the following overall discharge reaction:

Pb(s)+PbO2(s)+4H+(aq)+2SO42−(aq)→2PbSO4(s)+2H2O(l)Pb(s) + PbO_2(s) + 4H^+(aq) + 2SO_4^{2-}(aq) \rightarrow 2PbSO_4(s) + 2H_2O(l)

The standard cell potential is Ecell∘=2.05 VE^\circ_{cell} = 2.05 \text{ V}. Initially, the bulk electrolyte concentrations are [H+]=1.0 M[H^+] = 1.0 \text{ M} and [SO42−]=1.0 M[SO_4^{2-}] = 1.0 \text{ M}. During a rapid discharge at a constant current of I=2.0 AI = 2.0 \text{ A}, severe concentration polarization occurs, causing the local surface concentrations at the electrodes to drop to [H+]surf=0.1 M[H^+]_{surf} = 0.1 \text{ M} and [SO42−]surf=0.01 M[SO_4^{2-}]_{surf} = 0.01 \text{ M}.

Given the activation overpotential ηact=0.10 V\eta_{act} = 0.10 \text{ V} and the internal resistance of the cell Rint=0.05 ΩR_{int} = 0.05 \ \Omega, calculate the actual terminal voltage (VcellV_{cell}) of the battery during this discharge.

(Assume 2.303RTF=0.06 V\frac{2.303 RT}{F} = 0.06 \text{ V} at 298 K298 \text{ K})

Options

  • A.

    1.85 \text{ V}

  • B.

    1.76 \text{ V}

  • C.

    1.61 \text{ V}

  • D.

    2.01 \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

Secondary Battery Discharge Cycles|Nernst Equation Concentration Dependence|Electrode Potential Dependencies

Why This Question Is Tricky

Common Mistakes

Students often mistakenly use bulk concentrations in the Nernst equation, ignoring that electrochemical reactions are interfacial phenomena.

During rapid discharge, the local concentration of reactants at the electrode surface depletes (Concentration Polarization), significantly altering the reaction quotient QQ.

This problem tests the ability to bridge thermodynamic idealization with electrochemical kinetics by forcing the calculation of the true surface potential EsurfE_{surf} before applying kinetic losses (activation overpotential and Ohmic drop) to find the terminal voltage.

Failing to account for the 4th and 2nd power stoichiometric dependencies of H+H^+ and SO42−SO_4^{2-} respectively, or using bulk values, leads to incorrect higher voltage estimates.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterElectrochemistry - Class 12
ConceptSecondary Battery Discharge Cycles
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree