Reaction Rates and Rate Laws - Reaction Kinetics - Life Sciences Previous Year Questions

1

2008 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2008

The plot of concentration of A against time is a straight line with negative slope for the reaction:
\[A \rightarrow \text{products}\]
The order of the reaction is

A

\(-1\)

B

0

C

1

D

2

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2

2008 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2008

For a first order reaction at a particular temperature, the half-life was found to be \((100 \ln2)\) seconds. The specific rate constant of the reaction is

A

0.01 \(s^{-1}\)

B

100 \(s^{-1}\)

C

230 \(s^{-1}\)

D

693 \(s^{-1}\)

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3

2008 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2008

The rate constant of the backward reaction (k_b) is

A

5.26 x 10⁻² s⁻¹

B

1 x 10⁻² s⁻¹

C

4.35 x 10⁻² s⁻¹

D

1 x 10⁻⁴ s⁻¹

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4

2009 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2009

For a second order reaction, \( R \xrightarrow{k} P \), the relation between half-life time ( \( t_{1/2} \) ) and the initial reactant concentration [\( R_0 \)] is

A

\(t_{1/2} = \frac{\ln 2}{k} \)

B

\(t_{1/2} = \frac{2}{k[R]_0} \)

C

\(t_{1/2} = \frac{1}{k[R]_0^2} \)

D

\(t_{1/2} = \frac{1}{k[R]_0} \)

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5

2011 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2011

If the concentration of KOH in the reaction mixture is doubled, the rate of the reaction will be

A

decreased to one-half

B

the same

C

increased by two-times

D

increased by four-times

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6

2013 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2013

Velocity of an object fired directly in upward direction is given by \( V = 80 – 32 t \), where \( t \) (time) is in seconds. When will the velocity be between 32 m/sec and 64 m/sec?

A

(1, 3/2)

B

(1/2, 1)

C

(1/2, 3/2)

D

(1, 3)

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7

2013 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2013

The rate of a chemical reaction is tripled when the temperature of the reaction is increased from 298 K to 308 K. The activation energy (in kcal mol^-1 K^-1, up to one decimal place) for the reaction is (Given R = 1.987 cal mol^-1 K^-1) ________________

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8

2014 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2014

For a first order reaction, the time required for 50% completion is 20 minutes. The time required for 99.9% completion of the reaction is _____ minutes.

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9

2016 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2016

‘A harmful substance persists in the environment for a very long period of time’. The UNACCEPTABLE statement for this fact is

A

The substance degrades by second-order kinetics

B

The substance degrades by first-order kinetics

C

The substance is not biodegradable

D

The substance has long half-life

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10

2017 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2017

For a reaction A + B → products, the following data was obtained.

[A]₀ (M)	[B]₀ (M)	Initial rate
0.1	0.1	r
0.2	0.1	4r
0.1	0.2	2r

A₀ and B₀ are initial concentrations of A and B, respectively. The overall order of the reaction is

A

2

B

3

C

4

D

6

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11

2018 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2018

The activation energy (Ea) values for two reactions carried out at 25 °C differ by 5.0 kJ mol⁻¹. If the pre-exponential factors (A₁ and A₂) for these two reactions are of the same magnitude, the ratio of rate constants (k₁/k₂) is ______ (up to two decimal places). (Given: Gas constant R = 8.314 J K⁻¹ mol⁻¹)

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12

2019 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2019

For the reaction mechanism, 2X ⇌ Y (For this step, assume K_eq = [Y]/[X]^2) Y → P (k: rate constant for this step) the rate law is .

A

\(\frac{d[P]}{dt} = K_{eq}[Y]\)

B

\(\frac{d[P]}{dt} = k [X]^2\)

C

\(\frac{d[P]}{dt} = k K_{eq}[Y]\)

D

\(\frac{d[P]}{dt} = k K_{eq} [X]^2\)

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13

2020 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2020

A molecule in solution crystallizes into two different crystal forms with rate constants of 0.02 s⁻¹ and 0.13 s⁻¹. If the crystallization is assumed to be under kinetic control, then the half-life (in seconds, rounded off to one decimal place) of the molecule is ______.

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14

2020 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2020

The activation energy ($E_a$) estimated for a reaction from the Arrhenius equation is 21 kJ mol⁻¹. If the frequency factor is assumed to be independent of temperature, then the ratio of the rate constants determined at 298 K and 260 K is ______ (rounded off to two decimal places). (Given: Gas constant, R = 8.315 J K⁻¹ mol⁻¹)

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15

2021 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2021

The time taken by a first order reaction to reach 90% completion is 20 s.
The time taken for the reaction to reach 50% completion is ______ s
(rounded off to the closest integer).

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16

2021 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2021

For a reaction, X → Products
Group I contains three plots of reactant concentrations as functions of time, where x = concentration of reactant X at time t, x₀ = concentration of reactant X at initial time, t = 0. Group II gives a list of different orders of reaction. Match the plots with the order of the reaction.

A

(P) – (1), (Q) – (2), (R) – (3)

B

(P) – (3), (Q) – (2), (R) – (1)

C

(P) – (2), (Q) – (3), (R) – (1)

D

(P) – (2), (Q) – (1), (R) – (3)

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17

2022 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2022

Consider a second order reaction, \(2A \longrightarrow Product\)
The concentration of A is represented as [A].
Which of the following is the CORRECT plot for determining the rate constant for the above reaction?

A

plot of \(\log[A]\) vs time, starting at (0,0)

B

plot of \([A]\) vs time, starting at (0,0)

C

plot of \(1/[A]\) vs time, starting at (0,0)

D

plot of \(1/[A]^2\) vs time, starting at (0,0)

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18

2023 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2023

Orange juice is packaged aseptically and stored under ambient conditions. The degradation of vitamin C in the juice occurs during storage and it follows first order reaction kinetics. The degradation rate constant is \(5.2\times10^{-3}\) day\(^{-1}\). The half-life of vitamin C in days is __________ (in integer).

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19

2024 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2024

The initial rate of a reaction triples when the concentration of a reactant, A, is doubled. The order of the reaction with respect to A is ______ (rounded off to 2 decimal places).

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20

2025 · Life Sciences · Reaction Kinetics · Reaction Rates and Rate Laws

Life Sciences (XL) 2025

The temperature dependence of reaction rates is generally given by the Arrhenius equation. A plot of \( \ln k_r \) against \( 1/T \) is a straight line from which the pre-exponential factor ‘A’ and the activation energy ‘\( E_a \)’ can be determined.
The CORRECT option regarding this plot is

A

Slope: –\(E_a \)/R; Intercept on the y-axis: ln A

B

Slope: +\(E_a \)/2.303R; Intercept on the y-axis: A

C

Slope: +\(E_a \)/R; Intercept on the y-axis: A

D

Slope: –\(E_a \)/2.303R; Intercept on the y-axis: ln A

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