Explore popular questions from Chemical Kinetics for JEE Advanced. This collection covers Chemical Kinetics previous year JEE Advanced questions hand picked by experienced teachers.

## Chemistry

Chemical Kinetics

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Q 1. The rate constant, the activation energy and the Arrhenius parameter of a chemical reaction at {tex} 25 ^ { \circ } \mathrm { C } {/tex} are {tex} 3.0 \times 10 ^ { - 4 }\ \mathrm { s } ^ { - 1 } , {/tex} {tex} 104.4\ \mathrm { kJ }\ \mathrm { mol } ^ { - 1 } {/tex} and {tex} 6.0 \times 10 ^ { 14 }\ \mathrm { s } ^ { - 1 } {/tex} respectively. The value of the rate constant as {tex} \mathrm { T } \rightarrow \infty {/tex} is,

A

{tex} 2.0 \times 10 ^ { 18 } \mathrm { s } ^ { - 1 } {/tex}

{tex} 6.0 \times 10 ^ { 14 } \mathrm { s } ^ { - 1 } {/tex}

C

infinity

D

{tex} 3.6 \times 10 ^ { 30 } \mathrm { s } ^ { - 1 } {/tex}

##### Explanation

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Q 2. In a first order reaction the concentration of reactant decreases from {tex} 800\ \mathrm { mol } / \mathrm { dm } ^ { 3 } {/tex} to {tex} 50\ \mathrm { mol } / \mathrm { dm } ^ { 3 } {/tex} in {tex} 2 \times 10 ^ { 4 } \mathrm { sec } . {/tex} The rate constant of reaction in {tex} \mathrm { sec } ^ { - 1 }\ \mathrm { is: } {/tex}

A

{tex} 2 \times 10 ^ { 4 } {/tex}

B

{tex} 3.45 \times 10 ^ { - 5 } {/tex}

{tex} 1.386 \times 10 ^ { - 4 } {/tex}

D

{tex} 2 \times 10 ^ { - 4 } {/tex}

##### Explanation

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Q 3. {tex} \mathrm { Ag } ^ { + } + \mathrm { NH } _ { 3 } \rightleftharpoons \left[ \mathrm { Ag } \left( \mathrm { NH } _ { 3 } \right) \right] ^ { + } ; k _ { 1 } = 6.8 \times 10 ^ { - 3 } {/tex}
{tex} \left[ \mathrm { Ag } \left( \mathrm { NH } _ { 3 } \right) \right] ^ { + } + \mathrm { NH } _ { 3 } \rightleftharpoons \left[ \mathrm { Ag } \left( \mathrm { NH } _ { 3 } \right) _ { 2 } \right] ^ { + } ; \mathrm { k } _ { 2 } = 1.6 \times 10 ^ { - 3 } {/tex}
then the formation constant of {tex} \left[ \mathrm { Ag } \left( \mathrm { NH } _ { 3 } \right) _ { 2 } \right] ^ { + } {/tex} is

A

{tex} 6.8 \times 10 ^ { - 6 } {/tex}

{tex} 1.08 \times 10 ^ { - 5 } {/tex}

C

{tex} 1.08 \times 10 ^ { - 6 } {/tex}

D

{tex} 6.8 \times 10 ^ { - 5 } {/tex}

##### Explanation

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Q 4. In the reaction,
{tex} \mathrm { P } + \mathrm { Q } \longrightarrow \mathrm { R } + \mathrm { S } {/tex}
The time taken for {tex} 75 \% {/tex} reaction of {tex} \mathrm { P } {/tex} is twice the time taken for {tex} 50 \% {/tex} reaction of {tex} \mathrm { P } {/tex}. The concentration of {tex} \mathrm { Q } {/tex} varies with reaction time as shown in the figure. The overall order of the reaction is

A

2

B

3

C

0

1

##### Explanation

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Q 5. For the elementary reaction {tex} M \rightarrow N {/tex}, the rate of disappearance of {tex} M {/tex} increases by a factor of 8 upon doubling the concentration of {tex} M . {/tex} The order of the reaction with respect to {tex} M {/tex} is

A

4

3

C

2

D

1

##### Explanation

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Q 6.

What can you say about the existence of A if the potential energy diagram for the reaction

looks like

A

A will exist

A will not exist

C

B will not exist

D

A and B are in equilibrium

##### Explanation

Factual statement

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Q 7.

A catalyst only

A

Decreases activation energy

B

Increases activation energy

Both of them

D

Comes to equilibrium

##### Explanation

Factual statement

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Q 8.

Product, . After 10 min reaction is 10% completed. If , then is approximately

A

0.693 min

B

69.3 min

66.0 min

D

0.0693 min

##### Explanation

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Q 9.

For an endothermic reaction, where represnts the enthalpy of reaction in , the minimum value for the energy of activation will be

A

Less than

B

Zero

More than

D

Equal to

##### Explanation

For endothermic reaction:

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Q 10.

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

A

60 min

B

15 min

C

7.5 min

30 min

##### Explanation

Thus, total time min

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Q 11.

For a first order reaction , the temperature dependent rate constant was found to follow the equation.

The pre-exponential factor and the activation energy , respectively, are

A

B

C

##### Explanation

Comparing the slope and intercept of the given equation with the following Arrhenius equation :

Hence,

Comparing slope gives 38.3 kJ/mol

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Q 12.

In a second order reaction, 20% of a substance is dissociated in 40 min. The time taken by 80% of its dissociation is

A

160 min

640 min

C

200 min

D

320 min

##### Explanation

For second order reaction,

When

(i)

When

(ii)

From equations (i) and (ii),

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Q 13.

For the chemical reaction , rate of the reaction is increased by 2.82 times when the concentration of A is doubled and increased by 9 times when the concentration of B was tripled. What is the order with respect to B, A, and the total order?

A

3/2, 2;7/2

2, 3/2; 7/2

C

5/2, 2:9/2

D

2, 5/2; 9/2

##### Explanation

(i)

(ii)

(iii)

(iv)

Sove for and

Order w.r.t.

Total order

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Q 14.

What specific name can be given to the following sequence of steps:

A

Fluorescence

B

Phosphorescence

Photosensitization

D

Chemiluminescence

##### Explanation

Factual statement

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Q 15.

For a second order reaction . Its half life period is

B

C

D

##### Explanation

Second order reactions: Reaction rate depends upon the concentration of two reactants

and are the concentration of A and B after time interval .

When concentrations of both the reactants are same,

( is the concentration changed in time interval )

Half-life period, i.e., inversely proportional to initial concentration. The units of are liter

Plot of rate versus

Plot of versus

Plot of versus

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Q 16.

It is generalized that a increase in temperature causes the rate of reactions to double. Applied to a reaction at 295 K, what is the value of ?

A

B

C

##### Explanation

Formula and Concepts”

Only reactions whose falls in the range of or are found to double their rate for rise in temperature i.e., from 298 to 308 K

Alternatively

Use Arrhenius equation

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Q 17.

A Geigger Muller counter is used to study the radioactive process. In the absence of radioactive substance A, it counts 3 disintegration per second (dps). At the start in the presence of A, it records 23 dps; and after 10 min 13 dps

• What does it count after 20 min?

• What is the half life of A?

• a)

8 dps, 10 min

B

5 dps, 10 min

C

5 dps, 20 min

D

5 dps, 5 min

##### Explanation

In the absence of A,3 dps is zero error, hence

Initial count dps

After 10 min dps

After 20 min dps (recorded dps)

(50% fall in 10 min, min)

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Q 18.

The reaction kinetics can be studied by

A

Measurement of pH

Titration with hypo after adding KI

C

Both correct

D

None is correct

##### Explanation

Cl attached to N in reactant oxidizes KI to which can be determined by hypo

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Q 19.

Diazonium salt decomposes as

At , the evolution of becomes two times faster when the initial concentration of the salt is doubled. Thus, it is

A first order reaction

B

A second order reaction

C

Independent of the initial concentration of reactant

D

A zero order reaction

##### Explanation

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Q 20.

In a reaction carried out at 500 K, 0.001% of the total number of collisions are effective. The energy of activation of the reaction is approximately

A

C

D

Zero

##### Explanation

The fraction of molecules having energy equal to or greater than is:

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Q 21.

If a reaction involves gaseous reactants and products, the units of its rate are

A

atm

B

atm-s

atm-

D

##### Explanation

Factual statement

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Q 22.

For a reaction Products, the rate law expression is . Then

A

B

may or may not be equal to

D

##### Explanation

Factual statement

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Q 23.

The rate constant, the activation energy, and the Arrhenius parameter of a chemical reaction at are , and , respectively. The value of the rate constant as is

A

C

Infinity

D

##### Explanation

As

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Q 24.

In an acidic medium, the rate of reaction between and ions is given by the expression

It means

A

The rate constant of overall reaction is

B

The rate of reaction is independent of the concentration of acid

C

The change in pH of the solution will not affect the rate

Doubling the concentration of ions will increase the reaction rate by 4 times

##### Explanation

Order w.r.t.

Hence, doubling the concentration of ions will increase the reaction rate by 4 times

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Q 25.

The quantum yield of photosynthesis of

B

C

D

None

##### Explanation

Negative catalyst or inhibitors are those substance which decrease the rate of a reaction