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Question #44049

Difficulty: 8/10 | 🟢 Free

The Question

Consider a galvanic cell operating at 300 K300\text{ K} with the following balanced cell reaction:

\ceM(s)+X2+(aq)<=>M2+(aq)+X(s)\ce{M(s) + X^{2+}(aq) <=> M^{2+}(aq) + X(s)}

The standard cell potential at 300 K300\text{ K} is E∘=0.10 VE^{\circ} = 0.10\text{ V}. The temperature coefficient of the standard cell potential at constant pressure is (∂E∘∂T)P=−5.0×10−4 V K−1\left(\frac{\partial E^{\circ}}{\partial T}\right)_P = -5.0 \times 10^{-4}\text{ V K}^{-1}.

Assuming that the standard enthalpy (ΔH∘\Delta H^{\circ}) and standard entropy (ΔS∘\Delta S^{\circ}) of the reaction are independent of temperature, determine the standard enthalpy of the reaction at 300 K300\text{ K} and the temperature (TeqT_{eq}) at which the cell reaction reverses its direction of spontaneity under standard conditions.

(Given: Faraday's constant F=96500 C mol−1F = 96500\text{ C mol}^{-1})

Options

  • A.

    ΔH∘=−48.25 kJ mol−1\Delta H^{\circ} = -48.25\text{ kJ mol}^{-1}, Teq=500 KT_{eq} = 500\text{ K}

  • B.

    ΔH∘=−19.30 kJ mol−1\Delta H^{\circ} = -19.30\text{ kJ mol}^{-1}, Teq=200 KT_{eq} = 200\text{ K}

  • C.

    ΔH∘=−24.12 kJ mol−1\Delta H^{\circ} = -24.12\text{ kJ mol}^{-1}, Teq=500 KT_{eq} = 500\text{ K}

  • D.

    ΔH∘=+9.65 kJ mol−1\Delta H^{\circ} = +9.65\text{ kJ mol}^{-1}, Teq=100 KT_{eq} = 100\text{ K}

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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-Helmholtz Equation|Gibbs Energy and Spontaneity|Corrosion as Electrochemical Process

Why This Question Is Tricky

Common Mistakes

This problem tests the integration of electrochemistry with chemical thermodynamics via the Gibbs-Helmholtz equation.

The primary trap (Option B) is the assumption that ΔH∘≈ΔG∘\Delta H^{\circ} \approx \Delta G^{\circ}, which ignores the significant entropic contribution derived from the temperature coefficient of the cell.

A secondary trap (Option C) is forgetting the stoichiometric number of electrons transferred (n=2n=2) in the Nernstian derivation of entropy.

The problem forces students to recognize that a spontaneous reaction at room temperature can become non-spontaneous at higher temperatures if the entropy change is negative, physically manifested as a negative temperature coefficient of the cell potential.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterThermodynamics - Class 11 Part 1
ConceptGibbs-Helmholtz Equation
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree