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Question #44827

Difficulty: 8/10 | 🟢 Free

The Question

The acid-catalyzed hydration of 1-methylcyclohexene to 1-methylcyclohexanol proceeds via a rate-determining protonation step. In pure water at 300 K300\text{ K} (viscosity η1=1.0 cP\eta_1 = 1.0\text{ cP}), the reaction exhibits an activation energy Ea=63.19 kJ mol−1E_a = 63.19\text{ kJ mol}^{-1} and a rate constant k1k_1.

To study solvent-solute dynamics, the reaction is transferred to a highly viscous glycerol-water mixture. In this medium, the dielectric constant remains identical to water, but the kinetics enter the Kramers high-friction regime. According to Kramers' theory, the Arrhenius pre-exponential factor AA becomes inversely proportional to the solvent viscosity (η\eta) due to the Franck-Rabinowitch caging effect.

At 330 K330\text{ K}, the viscosity of the glycerol-water mixture is η2=2.0 cP\eta_2 = 2.0\text{ cP}. Assuming EaE_a remains strictly constant across both media, what is the ratio of the rate constant in the viscous mixture at 330 K330\text{ K} (k2k_2) to k1k_1?

(Given: R=8.314 J K−1mol−1R = 8.314\text{ J K}^{-1}\text{mol}^{-1}, ln⁡(10)=2.303\ln(10) = 2.303)

Options

  • A.

    5.0

  • B.

    10.0

  • C.

    20.0

  • D.

    1.0

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Correct Answer

Step-by-Step Solution

Explanation

How the Examiner Thinks

Exception_Exposure

Learn to identify edge cases and boundary exceptions that JEE examiners hide in math problems.

Concepts Behind This Question

Arrhenius Pre-exponential Factor|Acid-Catalyzed Hydration Mechanism

Why This Question Is Tricky

Common Mistakes

This question tests the 'Chemical Exception' to the standard Arrhenius equation where the pre-exponential factor (A) is assumed constant.

In high-viscosity solvents, the reaction enters the Kramers high-friction regime, where the collision frequency drops due to the 'caging effect' (Franck-Rabinowitch effect).

Students must integrate this inverse viscosity dependence (A∝η−1A \propto \eta^{-1}) with the standard temperature-dependent exponential term.

A common trap is ignoring the solvent's effect on A (yielding 10.0) or misapplying the proportionality as direct instead of inverse (yielding 20.0).

Quick Facts About This Question

Question Information

SubjectChemistry
ChapterChemical Kinetics - Class 12
ConceptArrhenius Pre-exponential Factor
Difficulty8
Cognitive Load7
Target Solve Time160 sec
AccessFree