Chemical Kinetics MCQs Question and Answer in Engineering Chemistry

11

A reaction proceeds through the formation of an intermediate B in a unimolecular reaction \[A\xrightarrow{{{k_a}}}B\xrightarrow{{{k_b}}}C\]
The integrated rate law for this reaction is

A) $$\left[ A \right] = {\left[ A \right]_0}{e^{ - {k_a}t}}$$ B) $$\left[ A \right] = {\left[ A \right]_0}\left( {{e^{ - {k_a}t}} - {e^{ - {k_b}t}}} \right)$$ C) $$\left[ A \right] = \frac{{{{\left[ A \right]}_0}}}{2}\left( {1 + \frac{{{k_a}{e^{ - {k_b}t}} - {k_b}{e^{ - {k_a}t}}}}{{{k_a} - {k_b}}}} \right)$$ D) $$\left[ A \right] = {\left[ A \right]_0}\left( {1 + {e^{ - {k_a}t}} - {e^{ - {k_b}t}}} \right)$$

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Answer & Solution

Answer: Option A

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12

If k_a ≫ k_b, then concentration versus time plot for the reaction is

A)

B)

C)

D)

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Answer & Solution

Answer: Option B

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13

In a homogeneous catalytic reaction, 1.0 M of a substrate band 1.0 μM of a catalyst yields 1.0 mM of a product in 10 s. The turnover frequency (TOF) of the reaction (S^-1) is

A) 10^-2 B) 10² C) 10^-3 D) 10³

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Answer & Solution

Answer: Option B

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14

For the reaction, P + Q + R → S, experimental data for the measured initial rates is given below:

Expt.	Initial conc. P (M)	Initial conc. Q (M)	Initial conc. R (M)	Initial rate (m/s)
1	0.2	0.5	0.4	8.0 × 10^-5
2	0.4	0.5	0.4	3.2 × 10^-4
3	0.4	2.0	0.4	1.28 × 10^-3
4	0.1	0.25	1.6	4.0 × 10^-5

The order of the reaction with respect to P, Q and R respectively, is

A) 2, 2, 1 B) 2, 1, 2 C) 2, 1, 1 D) 1, 1, 2

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Answer & Solution

Answer: Option C

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15

A reaction follows second order rate law, $$\frac{{ - d\left[ A \right]}}{{dt}} = k{\left[ A \right]^2},$$ if

A) a plot of [A] versus t is a straight line B) a plot of 1/[A] versus t is a straight line C) a plot of ln[A] versus t is a straight line D) a plot of e^[A] versus t is a straight line

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Answer & Solution

Answer: Option B

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16

The half-life (t_1/2) for the hydrolysis of an ester varies with the initial concentration of the reactant ([E]₀) as follows:

[E]₀/10 mol/L	5.0	4.0	3.0
t_1/2/s	240	300	400

The order of the reaction is

A) 0 B) 1 C) 2 D) 3

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Answer & Solution

Answer: Option C

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17

The specific rate constant of decomposition of a compound is represented by $$\ln k = 5.0 - \frac{{12000}}{T}$$
The activation energy of decomposition foe this compound at 300 K is

A) 24 kcal/mol B) 12 kcal/mol C) 24 cal/mol D) 12 cal/mol

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Answer & Solution

Answer: Option A

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18

In a consecutive first order reaction,
(where k₁ and k₂ are the respective rate constants) species B has transient existence. Therefore,

A) k₁ ≈ k₂ B) k₁ = 2k₂ C) k₁ ≫ k₂ D) k₁ ≪ k₂

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Answer & Solution

Answer: Option D

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19

The fluorescence life time of a molecule in solution is 10 ns. If the fluorescence quantum yield is 0.1, the rate constant of fluorescence decay is

A) 1 × 10⁹ s^-1 B) 1 × 10⁸ s^-1 C) 1 × 10⁷ s^-1 D) 9 × 10⁷ s^-1

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Answer & Solution

Answer: Option C

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20

The value of the rate constant for the gas phase reaction, 2NO₂ + F₂ → 2NO₂F is 38 dm³ mol^-1 s^-1 at 300K. The order of the reaction is

A) 0 B) 1 C) 2 D) 3

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Answer & Solution

Answer: Option C

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