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Question #44220

Difficulty: 8/10 | 🟢 Free

The Question

Consider the acid-catalyzed esterification of octadecanoic acid with octan-1-ol to form octyl octadecanoate and water. At 298 K298\text{ K}, the standard enthalpy and entropy of the reaction producing liquid water are ΔHrxn∘=−12.0 kJ mol−1\Delta H^\circ_{rxn} = -12.0\text{ kJ mol}^{-1} and ΔSrxn∘=−10.0 J K−1 mol−1\Delta S^\circ_{rxn} = -10.0\text{ J K}^{-1}\text{ mol}^{-1}, respectively.

The standard enthalpy of vaporization of water is ΔHvap∘=42.0 kJ mol−1\Delta H^\circ_{vap} = 42.0\text{ kJ mol}^{-1} and its standard entropy of vaporization is ΔSvap∘=110.0 J K−1 mol−1\Delta S^\circ_{vap} = 110.0\text{ J K}^{-1}\text{ mol}^{-1}.

The reaction is carried out at 400 K400\text{ K} in a continuous flow reactor. Due to the high boiling points of the organic species, they remain entirely in the liquid phase, but water is formed exclusively in the vapor phase. Assuming all standard enthalpies and entropies are independent of temperature, what is the value of ln⁡K\ln K for this specific equilibrium at 400 K400\text{ K}?

(RR is the universal gas constant in J K−1 mol−1\text{J K}^{-1}\text{ mol}^{-1})

Options

  • A.

    25R\frac{25}{R}

  • B.

    20R\frac{20}{R}

  • C.

    −85R-\frac{85}{R}

  • D.

    15R\frac{15}{R}

Check Your Answer

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

Acid-Catalyzed Hydration Mechanism|Esterification Reversibility|First Law Consistency

Why This Question Is Tricky

Common Mistakes

This problem tests the 'Water Activity Under First Law Constraints' trap.

Students frequently calculate high-temperature equilibrium constants by blindly plugging standard table values (which assume liquid water as the product) into the Gibbs free energy equation, yielding Option B (20/R).

By using heavy organic molecules (octadecanoic acid and octan-1-ol), the liquid state of the organics is realistically maintained at 400 K, making the vaporization of water the sole, critical thermodynamic correction required.

Failing to account for the heat of vaporization and entropy of vaporization of water violates the First and Second Laws of Thermodynamics for the actual reaction coordinate.

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterThermodynamics - Class 11 Part 1
ConceptFirst Law Consistency
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree