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Question #44738

Difficulty: 8/10 | 🟢 Free

The Question

An aqueous solution of 1.0 M \ceNaCl1.0\text{ M } \ce{NaCl}, buffered at pH=7.0\text{pH} = 7.0, is electrolyzed at 298 K298\text{ K} using smooth Platinum electrodes. A constant current of 10.0 A10.0\text{ A} is passed for 965 s965\text{ s}.

Given standard reduction potentials at 298 K298\text{ K}: E\ceCl2(g)/\ceCl−(aq)∘=+1.36 VE^\circ_{\ce{Cl2(g)}/\ce{Cl^- (aq)}} = +1.36\text{ V} E\ceO2(g),\ceH+(aq)/\ceH2O(l)∘=+1.23 VE^\circ_{\ce{O2(g)}, \ce{H^+ (aq)}/\ce{H2O(l)}} = +1.23\text{ V} E\ceH+(aq)/\ceH2(g)∘=0.00 VE^\circ_{\ce{H^+ (aq)}/\ce{H2(g)}} = 0.00\text{ V}

Kinetic overpotentials (η\eta) on Pt under these conditions: η\ceO2=0.65 V\eta_{\ce{O2}} = 0.65\text{ V} η\ceCl2=0.05 V\eta_{\ce{Cl2}} = 0.05\text{ V} η\ceH2=0.00 V\eta_{\ce{H2}} = 0.00\text{ V}

Assume 2.303RTF=0.06 V\frac{2.303 RT}{F} = 0.06\text{ V} and 1 F=96500 C mol−11\text{ F} = 96500\text{ C mol}^{-1}. All gases are at 1 bar1\text{ bar}.

Calculate the total minimum electrical energy required to drive the cell and produce the major anodic product. (Assume 100% current efficiency).

Options

  • A.

    17.66 kJ

  • B.

    18.14 kJ

  • C.

    11.87 kJ

  • D.

    13.61 kJ

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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

Gibbs Energy and Spontaneity|Faraday's First and Second Laws|Electrolysis Product Prediction

Why This Question Is Tricky

Common Mistakes

This problem tests the critical intersection of Thermodynamics (Nernst Equation) and Kinetics (Overpotential) in electrolysis.

Students often calculate standard cell potentials, expecting spontaneity based purely on ΔG<0\Delta G < 0.

Here, thermodynamically, \ceO2\ce{O2} evolution is favored by 0.55 V0.55\text{ V} at pH=7\text{pH} = 7.

However, the 'Hidden Variable' is the kinetic overpotential on the Platinum electrode.

The high activation energy for \ceO2\ce{O2} formation shifts its discharge potential, making \ceCl2\ce{Cl2} the major product.

Failing to account for this kinetic reality leads to incorrect product prediction and energy calculation.

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Question Information

SubjectChemistry
ChapterElectrochemistry - Class 12
ConceptGibbs Energy and Spontaneity
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree