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Question #44831

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The Question

The diazotization of aniline ( $\ce{C6H5NH2}$ ) with $\ce{NaNO2}$ and aqueous $\ce{HCl}$ is optimally carried out at $278\text{ K}$ , where the stable benzenediazonium chloride accumulates at a rate $r_1$ . A student attempts to optimize the process by raising the reaction temperature to $298\text{ K}$ . Assuming a temperature coefficient $\mu = 2$ for the reaction kinetics, the student predicts a new accumulation rate $r_{predicted}$ for the diazonium salt. However, experimentally, the actual accumulation rate of the diazonium salt at $298\text{ K}$ is found to be $r_{actual}$ , accompanied by the vigorous evolution of a colorless gas and the formation of a major organic product $\textbf{P}$ .

Which of the following correctly identifies $r_{predicted}$ , $r_{actual}$ , and the product $\textbf{P}$ ?

Options

A.
$r_{predicted} = 4r_1$ ; $r_{actual} \approx 0$ ; $\textbf{P} = \text{Phenol}$
B.
$r_{predicted} = 2r_1$ ; $r_{actual} = 2r_1$ ; $\textbf{P} = \text{Chlorobenzene}$
C.
$r_{predicted} = 4r_1$ ; $r_{actual} = 4r_1$ ; $\textbf{P} = \text{Benzenediazonium chloride}$
D.
$r_{predicted} = 4r_1$ ; $r_{actual} \approx 0$ ; $\textbf{P} = p\text{-Aminoazobenzene}$

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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

Temperature Coefficient (Q10)|Diazotization Temperature Sensitivity

Why This Question Is Tricky

Common Mistakes

This question tests the 'Lethal Collision' trap, where students blindly apply mathematical kinetic models (like the $Q_{10}$ temperature coefficient) without accounting for the thermal instability of the reaction intermediate.

While the Arrhenius equation predicts a four-fold increase in the reaction rate, the arenediazonium salt degrades rapidly above $5^\circ\text{C}$ ( $278\text{ K}$ ).

This creates a kinetic cliff where the effective yield and accumulation rate of the desired product drop to zero, overriding the theoretical kinetic extrapolation.

It also tests the competing pathways at higher temperatures, where hydrolysis to phenol dominates over diazo coupling in strongly acidic media.

Quick Facts About This Question

Question Information

Subject	Chemistry
Chapter	Chemical Kinetics - Class 12
Concept	Temperature Coefficient (Q10)
Difficulty	8
Cognitive Load	7
Target Solve Time	160 sec
Access	Free