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Question #44843

Difficulty: 8/10 | 🟢 Free

The Question

A 1.0 \mumol1.0 \text{ \mu mol} sample of a pure radioisotope \ceZAX\ce{^{A}_{Z}X} (t1/2=100 mint_{1/2} = 100 \text{ min}) is placed in a specialized reactor. It undergoes α\alpha-decay with a mass defect of 0.005 amu0.005 \text{ amu} per disintegration. The energy released is captured with 40%40\% efficiency and used to drive the electrolysis of water (\ceH2O(l)−>H2(g)+1/2O2(g)\ce{H2O(l) -> H2(g) + 1/2 O2(g)}) at a constant applied potential of 1.5 V1.5 \text{ V}.

Assume the nuclear decay can be modeled as a thermodynamic process. Calculate the volume of \ceH2(g)\ce{H2(g)} collected at 300 K300 \text{ K} and 1 atm1 \text{ atm} after 200 min200 \text{ min}, and determine the equivalent standard cell potential (Eeq∘E^\circ_{eq}) for the decay of 1 mole of XX, assuming it acts as a 2-electron spontaneous process (ΔGdecay∘=−nFEeq∘\Delta G^\circ_{decay} = -n F E^\circ_{eq}).

(Given: 1 amu≡1000 MeV1 \text{ amu} \equiv 1000 \text{ MeV}, 1 eV=1.6×10−19 J1 \text{ eV} = 1.6 \times 10^{-19} \text{ J}, NA=6.0×1023 mol−1N_A = 6.0 \times 10^{23} \text{ mol}^{-1}, F=96000 C mol−1F = 96000 \text{ C mol}^{-1}, R=0.082 L atm K−1 mol−1R = 0.082 \text{ L atm K}^{-1} \text{ mol}^{-1}. Assume ΔGdecay∘≈ΔHdecay∘\Delta G^\circ_{decay} \approx \Delta H^\circ_{decay})

Options

  • A.

    12.3 L12.3 \text{ L} and +2.5×106 V+2.5 \times 10^6 \text{ V}

  • B.

    12.3 L12.3 \text{ L} and −2.5×106 V-2.5 \times 10^6 \text{ V}

  • C.

    24.6 L24.6 \text{ L} and +2.5×106 V+2.5 \times 10^6 \text{ V}

  • D.

    16.4 L16.4 \text{ L} and −1.25×106 V-1.25 \times 10^6 \text{ V}

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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

Radioactive Decay as Kinetics|Gibbs Energy and Spontaneity|Standard Electrode Potential Sign Conventions

Why This Question Is Tricky

Common Mistakes

This problem tests the intersection of First-Order Nuclear Kinetics, Faraday's Laws of Electrolysis, and Thermodynamics.

The primary trap lies in the sign convention of Gibbs Free Energy and Cell Potential.

Students often confuse the non-spontaneous nature of the driven electrolytic cell (ΔG>0\Delta G > 0) with the highly spontaneous nature of the nuclear decay powering it (ΔG<0\Delta G < 0, hence Eeq∘>0E^\circ_{eq} > 0).

Secondary traps include forgetting the n=2n=2 factor for the production of one mole of \ceH2\ce{H2} gas, and failing to account for the un-decayed fraction of the isotope after 2 half-lives.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterChemical Kinetics - Class 12
ConceptRadioactive Decay as Kinetics
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree