Chemical Kinetics · JEE Main previous year questions

1. A.${\mu }_B>{\mu }_A$ and ${\mathrm{K}}_{\mathrm{e}}(\mathrm{A})>{\mathrm{K}}_{\mathrm{e}}(\mathrm{B})$
2. B.${\mu }_A>{\mu }_B$ and ${\mathrm{K}}_{\mathrm{e}}(\mathrm{B})>{\mathrm{K}}_{\mathrm{e}}(\mathrm{A})$
3. C.${\mu }_B>{\mu }_A$ and ${\mathrm{K}}_{\mathrm{e}}(\mathrm{B})>{\mathrm{K}}_{\mathrm{e}}(\mathrm{A})$
4. D.${\mu }_A>{\mu }_B$ and ${\mathrm{K}}_{\mathrm{e}}(\mathrm{A})>{\mathrm{K}}_{\mathrm{e}}(\mathrm{B})$

For the reaction of ${\mathrm{H}}_2$ with ${\mathrm{I}}_2$, the rate constant is $2.5\times 10^{-4}\mathrm{d}{\mathrm{m}}^3\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{s}}^{-1}$ at $327^{\circ }\mathrm{C}$ and $1.0\mathrm{d}{\mathrm{m}}^3\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{s}}^{-1}$ at $527^{\circ }\mathrm{C}$. The activation energy for the reaction, in $\mathrm{kJ}\mathrm{mol}{\mathrm{e}}^{-1}$ is : ($\mathrm{R}=8.314\mathrm{J}{\mathrm{K}}^{-1}\mathrm{mo}{\mathrm{l}}^{-1}$ )

1. A.59
2. B.166
3. C.72
4. D.150

In the following reaction $$\mathrm{Carbonyl}\mathrm{compound}+\mathrm{MeOH}\stackrel{\mathrm{HCl}}{\rightleftharpoons }\mathrm{acetal}$$ Rate of the reaction is the highest for :

1. A.Propanal as substrate and methanol in stoichiometric amount.
2. B.Acetone as substrate and methanol in stoichiometric amount
3. C.Propanal as substrate and methanol in excess
4. D.Acetone as substrate and methanol in excess

Decomposition of X exhibits a rate constant of $0.05\mu g/year$. How many years are required for the decomposition of $5\mu \mathrm{g}$ of X into $2.5\mu \mathrm{g}$?

1. A.50
2. B.20
3. C.25
4. D.40

For a reaction consider the plot of $\ln k$ versus $1/T$ given in the figure. If the rate constant of this reaction at 400 K is $10^{-5}{\mathrm{s}}^{-1}$, then the rate constant at 500 K is – [Figure: straight line plot of $\ln k$ vs $1/T$, Slope = −4606 K]

1. A.$10^{-4}{\mathrm{s}}^{-1}$
2. B.$4\times 10^{-4}{\mathrm{s}}^{-1}$
3. C.$10^{-6}{\mathrm{s}}^{-1}$
4. D.$2\times 10^{-4}{\mathrm{s}}^{-1}$

The reaction $2\mathrm{X}\to \mathrm{B}$ is a zeroth order reaction. If the initial concentration of X is $0.2\text{ M}$, the half-life is $6\text{ h}$. When the initial concentration of X is $0.5\text{ M}$, the time required to reach its final concentration of $0.2\text{ M}$ will be:

1. A.$18.0\text{ h}$
2. B.$9.0\text{ h}$
3. C.$7.2\text{ h}$
4. D.$12.0\text{ h}$

The following results were obtained during kinetic studies of the reaction ; $$2\mathrm{A}+\mathrm{B}\to \text{Products}$$ $$\begin{array}{llll}\text{Experiment}& {\text{[A] (in mol L}}^{-1}\text{)}& {\text{[B] (in mol L}}^{-1}\text{)}& {\text{Initial Rate of reaction (in mol L}}^{-1}{\text{ min}}^{-1}\text{)}\\ \text{I}& 0.10& 0.20& 6.93\times 10^{-3}\\ \text{II}& 0.10& 0.25& 6.93\times 10^{-3}\\ \text{III}& 0.20& 0.30& 1.386\times 10^{-2}\end{array}$$ The time (in minutes) required to consume half of A is :

1. A.5
2. B.10
3. C.1
4. D.100

${\text{N}}_2{\text{O}}_5$ decomposes to ${\text{NO}}_2$ and ${\text{O}}_2$ and follows first order kinetics. After 50 minutes, the pressure inside the vessel increases from 50 mmHg to 87.5 mmHg. The pressure of the gaseous mixture after 100 minute at constant temperature will be :

1. A.175.0 mmHg
2. B.116.25 mmHg
3. C.136.25 mmHg
4. D.106.25 mmHg

At $518^{\circ }\text{C}$ the rate of decomposition of a sample of gaseous acetaldehyde initially at a pressure of 363 Torr, was $1.00\text{Torr}{\text{s}}^{-1}$ when 5% had reacted and $0.5\text{Torr}{\text{s}}^{-1}$ when 33% had reacted. The order of the reaction is

1. A.0
2. B.2
3. C.3
4. D.1

The rate of a reaction quadruples when the temperature changes from 300 to 310 K. The activation energy of this reaction is : (Assume activation energy and preexponential factor are independent of temperature; $\ln 2=0.693$; $\mathrm{R}=8.314\mathrm{J}\mathrm{mo}{\mathrm{l}}^{-1}{\mathrm{K}}^{-1}$)

1. A.$107.2\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
2. B.$53.6\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
3. C.$26.8\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
4. D.$214.4\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$

The rate of a reaction A doubles on increasing the temperature from 300 to 310 K. By how much, the temperature of reaction B should be Increased from 300 K so that rate doubles if activation energy of the reaction B is twice to that of reaction A.

1. A.9.84 K
2. B.4.92 K
3. C.2.45 K
4. D.19.67 K

Decomposition of ${\mathrm{H}}_2{\mathrm{O}}_2$ follows a first order reaction. In fifty minutes the concentration of ${\mathrm{H}}_2{\mathrm{O}}_2$ decreases from $0.5$ to $0.125\mathrm{M}$ in one such decomposition. When the concentration of ${\mathrm{H}}_2{\mathrm{O}}_2$ reaches $0.05\mathrm{M}$, the rate of formation of ${\mathrm{O}}_2$ will be :

1. A.$6.93\times 10^{-4}\mathrm{mol}\mathrm{mi}{\mathrm{n}}^{-1}$
2. B.$6.96\times 10^{-2}\mathrm{mol}\mathrm{mi}{\mathrm{n}}^{-1}$
3. C.$1.34\times 10^{-2}\mathrm{mol}\mathrm{mi}{\mathrm{n}}^{-1}$
4. D.$2.66\mathrm{L}\mathrm{mi}{\mathrm{n}}^{-1}$ at STP

The activation energy for a reaction which doubles the rate when the temperature is raised from 298 K to 308 K is

1. A.$59.2\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
2. B.$39.2\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
3. C.$52.9\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$
4. D.$29.5\mathrm{kJ}\mathrm{mo}{\mathrm{l}}^{-1}$

In a chemical reaction $A$ is converted into $B$. The rates of reaction, starting with initial concentrations of $A$ as $2\times 10^{-3}\mathrm{M}$ and $1\times 10^{-3}\mathrm{M}$, are equal to $2.40\times 10^{-4}\mathrm{M}{\mathrm{s}}^{-1}$ and $0.60\times 10^{-4}\mathrm{M}{\mathrm{s}}^{-1}$ respectively. The order of reaction with respect to reactant $A$ will be

1. A.0
2. B.1.5
3. C.1
4. D.2

The time for half life period of a certain reaction $\mathrm{A}\to \mathrm{products}$ is 1 hour. When the initial concentration of the reactant 'A', is $2.0\mathrm{mol}{\mathrm{L}}^{-1}$, how much time does it take for its concentration to come from 0.50 to $0.25\mathrm{mol}{\mathrm{L}}^{-1}$ if it is a zero order reaction ?

1. A.4 h
2. B.0.5 h
3. C.0.25 h
4. D.1 h

A reaction was found to be second order with respect to the concentration of carbon monoxide. If the concentration of carbon monoxide is doubled, with everything else kept the same, the rate of reaction will

1. A.remain unchanged
2. B.triple
3. C.increase by a factor of 4
4. D.double

Rate of a reaction can be expressed by Arrhenius equation as: $$k=A{e}^{-E/RT}$$ In this equation, E represents

1. A.the energy above which all the colliding molecules will react
2. B.the energy below which colliding molecules will not react
3. C.the total energy of the reacting molecules at a temperature, T
4. D.the fraction of molecules with energy greater than the activation energy of the reaction

The following mechanism has been proposed for the reaction of NO with $\mathrm{B}{\mathrm{r}}_2$ to form NOBr: $\mathrm{NO}(\mathrm{g})+\mathrm{B}{\mathrm{r}}_2(\mathrm{g})\rightleftharpoons \mathrm{NOB}{\mathrm{r}}_2(\mathrm{g})$ $\mathrm{NOB}{\mathrm{r}}_2(\mathrm{g})+\mathrm{NO}(\mathrm{g})\to 2NOBr(\mathrm{g})$ If the second step is the rate determining step, the order of the reaction with respect to NO(g) is

1. A.1
2. B.0
3. C.3
4. D.2

${\mathrm{t}}_{1/4}$ can be taken as the time taken for the concentration of a reactant to drop to $\frac{3}{4}$ of its initial value. If the rate constant for a first order reaction is $\mathrm{K}$, the ${\mathrm{t}}_{1/4}$ can be written as

1. A.$0.10/\mathrm{K}$
2. B.$0.29/\mathrm{K}$
3. C.$0.69/\mathrm{K}$
4. D.$0.75/\mathrm{K}$

In a first order reaction, the concentration of the reactant decreases from 0.8 M to 0.4 M in 15 minutes. The time taken for the concentration to change from 0.1 M to 0.025 M is

1. A.30 minutes
2. B.60 minutes
3. C.7.5 minutes
4. D.15 minutes

Rate of the reaction $$\mathrm{R}-\mathrm{C}(=\mathrm{O})-\mathrm{Z}+\mathrm{N}{\mathrm{u}}^{-}⟶\mathrm{R}-\mathrm{C}(=\mathrm{O})-\mathrm{Nu}+{\mathrm{Z}}^{-}$$ is fastest when $Z$ is

1. A.$\mathrm{O}{\mathrm{C}}_2{\mathrm{H}}_5$
2. B.$\mathrm{N}{\mathrm{H}}_2$
3. C.$\mathrm{Cl}$
4. D.$\mathrm{OCOC}{\mathrm{H}}_3$

Units of rate constant of first and zero order reactions in terms of molarity M unit are respectively

1. A.$\mathrm{se}{\mathrm{c}}^{-1},\mathrm{Mse}{\mathrm{c}}^{-1}$
2. B.$\mathrm{se}{\mathrm{c}}^{-1},\mathrm{M}$
3. C.$\mathrm{Mse}{\mathrm{c}}^{-1},\mathrm{se}{\mathrm{c}}^{-1}$
4. D.$\mathrm{M},\mathrm{se}{\mathrm{c}}^{-1}$

For the reaction $\mathrm{A}+2B\to \mathrm{C}$, rate is given by R = [A] [B]${}^2$ then the order of the reaction is

1. A.3
2. B.6
3. C.5
4. D.7

The differential rate law for the reaction ${\mathrm{H}}_2+{\mathrm{I}}_2\to 2HI$ is

1. A.$-\frac{d[H_2]}{dt}=-\frac{d[I_2]}{dt}=-\frac{d[HI]}{dt}$
2. B.$\frac{d[H_2]}{dt}=\frac{d[I_2]}{dt}=\frac{d[HI]}{dt}$
3. C.$\frac{1}{2}\frac{d[H_2]}{dt}=\frac{1}{2}\frac{d[I_2]}{dt}=-\frac{d[HI]}{dt}$
4. D.$-2\frac{d[H_2]}{dt}=-2\frac{d[I_2]}{dt}=\frac{d[HI]}{dt}$

If half-life of a substance is 5 yrs, then the total amount of substance left after 15 years, when initial amount is 64 grams is

1. A.16 grams
2. B.2 grams
3. C.32 grams
4. D.8 grams