Share

Books Shortlist

# NCERT solutions for Class 12 Chemistry chapter 4 - Chemical Kinetics

## Chapter 4: Chemical Kinetics

#### Chapter 4: Chemical Kinetics solutions [Pages 98 - 116]

Q 1 | Page 98

For the reaction R → P, the concentration of a reactant changes from 0.03 M to 0.02 M in 25 minutes. Calculate the average rate of reaction using units of time both in minutes and seconds.

Q 2 | Page 98

In a reaction, 2A → Products, the concentration of A decreases from 0.5 mol L−1 to 0.4 mol L−1 in 10 minutes. Calculate the rate during this interval?

Q 3 | Page 103

For a reaction, A + B → Product; the rate law is given by, r = k[A]^(1/2)[B]^2 . What is the order of the reaction?

Q 4 | Page 103

The conversion of molecules X to Y follows second order kinetics. If concentration of X is increased to three times how will it affect the rate of formation of Y?

Q 5 | Page 111

A first order reaction has a rate constant 1.15 10−3 s−1. How long will 5 g of this reactant take to reduce to 3 g?

Q 6 | Page 111

Time required to decompose SO2Cl2 to half of its initial amount is 60 minutes. If the decomposition is a first order reaction, calculate the rate constant of the reaction.

Q 7 | Page 116

What will be the effect of temperature on rate constant?

Q 8 | Page 116

The rate of the chemical reaction doubles for an increase of 10 K in absolute temperature from 298 K. Calculate Ea.

Q 9 | Page 116

The activation energy for the reaction 2HI(g) → H2 + I2(gis 209.5 kJ mol−1 at 581K. Calculate the fraction of molecules of reactants having energy equal to or greater than activation energy?

#### Chapter 4: Chemical Kinetics solutions [Pages 117 - 120]

Q 1.1 | Page 117

From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.

3 NO(g) → N2O (g) Rate = k[NO]2

Q 1.2 | Page 117

From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.

H2O(aq) + 3 I− (aq) + 2 H+ → 2 H2O (l) + I_3^- Rate = k[H2O2][I]

Q 1.3 | Page 117

From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.

CH3CHO(g) → CH4(g) + CO(g) Rate = [CH3CHO]3/2

Q 1.4 | Page 117

From the rate expression for the following reactions, determine their order of reaction and the dimensions of the rate constants.

C2H5Cl(g) → C2H4(g) + HCl(g) Rate = k [C2H5Cl]

Q 2 | Page 117

For the reaction: 2A + B → A2B  the rate = k[A][B]2 with k = 2.0 × 10−6 mol−2 L2 s−1. Calculate the initial rate of the reaction when [A] = 0.1 mol L−1, [B] = 0.2 mol L−1. Calculate the rate of reaction after [A] is reduced to 0.06 mol L−1.

Q 3 | Page 117

The decomposition of NH3 on platinum surface is zero order reaction. What are the rates of production of N2 and H2 if = 2.5 × 10−4 mol−1 L s−1?

Q 4 | Page 117

The decomposition of dimethyl ether leads to the formation of CH4, H2 and CO and the reaction rate is given by

Rate = [CH3OCH3]3/2 .The rate of reaction is followed by increase in pressure in a closed vessel, so the rate can also be expressed in terms of the partial pressure of dimethyl ether, i.e., Rate = k(p_(CH_3OCH_3))^(3/2)

If the pressure is measured in bar andtime in minutes, then what are the units of rate and rate constants?

Q 5 | Page 117

Mention the factors that affect the rate of a chemical reaction.

Q 6 | Page 118

A reaction is second order with respect to a reactant. How is the rate of reaction affected if the concentration of the reactant is (i) doubled (ii) reduced to half?

Q 8 | Page 118

In a pseudo first order hydrolysis of ester in water, the following results were obtained:

 t/s 0 30 60 90 [Ester]mol L−1 0.55 0.31 0.17 0.085

(i) Calculate the average rate of reaction between the time interval 30 to 60 seconds.

(ii) Calculate the pseudo first order rate constant for the hydrolysis of ester.

Q 9.1 | Page 118

A reaction is first order in A and second order in B. Write the differential rate equation.

Q 9.2 | Page 118

A reaction is first order in A and second order in B. How is the rate affected on increasing the concentration of B three times?

Q 9.3 | Page 118

A reaction is first order in A and second order in B. How is the rate affected when the concentrations of both A and B are doubled?

Q 10 | Page 118

In a reaction between A and B, the initial rate of reaction (r0) was measured for different initial concentrations of A and B as given below:

 A/ mol L−1 0.20 0.20 0.40 B/ mol L−1 0.30 0.10 0.05 r0/ mol L−1 s−1 5.07 × 10−5 5.07 × 10−5 1.43 × 10−4

What is the order of the reaction with respect to A and B?

Q 11 | Page 118

The following results have been obtained during the kinetic studies of the reaction:

2A + B → C + D

 Experiment A/ mol L−1 B/ mol L−1 Initial rate of formation of D/mol L−1 min−1 I 0.1 0.1 6.0 × 10−3 II 0.3 0.2 7.2 × 10−2 III 0.3 0.4 2.40 × 10−2 IV 0.4 0.1

Determine the rate law and the rate constant for the reaction.

Q 12 | Page 118

The reaction between A and B is first order with respect to A and zero order with respect to B. Fill in the blanks in the following table:

 Experiment A/ mol L−1 B/ mol L−1 Initial rate/mol L−1 min−1 I 0.1 0.1 2.0 × 10−2 II -- 0.2 4.0 × 10−2 III 0.4 0.4 -- IV -- 0.2 2.0 × 10−2
Q 13 | Page 119

Calculate the half-life of a first order reaction from their rate constants given below:

(i) 200 s−1 (ii) 2 min−1 (iii) 4 years−1

Q 14 | Page 119

The half-life for radioactive decay of 14C is 5730 years. An archaeological artifact containing wood had only 80% of the 14C found in a living tree. Estimate the age of the sample.

Q 15 | Page 119

The experimental data for decomposition of N2O5

[2N_2O_5 -> 4NO_2 + O_2] in gas phase at 318K are given below:

 t(s 0 400 800 1200 1600 2000 2400 2800 3200 10^2xx[N_2O_5]mol L^(-1) 1.63 1.36 1.14 0.93 0.78 0.64 0.53 0.43 0.35

(i) Plot [N2O5] against t.

(ii) Find the half-life period for the reaction.

(iii) Draw a graph between log [N2O5] and t.

(iv) What is the rate law?

(v) Calculate the rate constant.

(vi) Calculate the half-life period from and compare it with (ii).

Q 16 | Page 119

The rate constant for a first order reaction is 60 s−1. How much time will it take to reduce the initial concentration of the reactant to its 1/16th value?

Q 17 | Page 119

During nuclear explosion, one of the products is 90Sr with half-life of 28.1 years. If 1μg of 90Sr was absorbed in the bones of a newly born baby instead of calcium, how much of it will remain after 10 years and 60 years if it is not lost metabolically.

Q 20 | Page 119

For the decomposition of azoisopropane to hexane and nitrogen at 543 K, the following data are obtained.

 t (sec) P(mm of Hg) 0 35.0 360 54.0 720 63.0

Calculate the rate constant.

Q 21 | Page 119

The following data were obtained during the first order thermal decomposition of SO2Cl2 at a constant volume :SO2Cl2 (g) → SO2 (g) + Cl2 (g)

 Experiment Time/s–1 Total pressure/atm 1 0 0.5 2 100 0.6

Calculate the rate of the reaction when total pressure is 0.65 atm.

Q 21 | Page 119

The rate constant for the decomposition of N2O5 at various temperatures is given below:

 T/°C 0 20 40 60 80 10^5XXK/s^(-1) 0.0787 1.7 25.7 178 2140

Draw a graph between ln and 1/and calculate the values of and Ea. Predict the rate constant at 30º and 50ºC.

Q 23 | Page 120

The rate constant for the decomposition of hydrocarbons is 2.418 × 10−5 s−1 at 546 K. If the energy of activation is 179.9 kJ/mol, what will be the value of pre-exponential factor.

Q 24 | Page 120

Consider a certain reaction A → Products with = 2.0 × 10−2 s−1. Calculate the concentration of Aremaining after 100 s if the initial concentration of is 1.0 mol L−1.

Q 25 | Page 120

Sucrose decomposes in acid solution to give glucose and fructose according to the first order rate law. The half life of the reaction is 3 hours. Calculate fraction of sucrose which will remain after 8 hours.

Q 26 | Page 120

The decomposition of hydrocarbon follows the equation = (4.5 × 1011 s−1) e−28000 K/T

Calculate Ea.

Q 27 | Page 120

The rate constant for the first order decomposition of H2O2 is given by the following equation:

log = 14.34 − 1.25 × 10K/T. Calculate Ea for this reaction and at what temperature will its half-period be 256 minutes?

Q 28 | Page 120

The decomposition of A into product has value of as 4.5 × 103 s−1 at 10°C and energy of activation 60 kJ mol−1. At what temperature would be 1.5 × 104 s−1?

Q 29 | Page 120

The time required for 10% completion of a first order reaction at 298 K is equal to that required for its 25% completion at 308 K. If the value of is 4 × 1010 s−1. Calculate at 318 K and Ea.

Q 30 | Page 120

The rate of a reaction quadruples when the temperature changes from 293 K to 313 K. Calculate the energy of activation of the reaction assuming that it does not change with temperature.

## NCERT solutions for Class 12 Chemistry chapter 4 - Chemical Kinetics

NCERT solutions for Class 12 Chemistry chapter 4 (Chemical Kinetics) include all questions with solution and detail explanation. This will clear students doubts about any question and improve application skills while preparing for board exams. The detailed, step-by-step solutions will help you understand the concepts better and clear your confusions, if any. Shaalaa.com has the CBSE Chemistry Textbook for Class 12 solutions in a manner that help students grasp basic concepts better and faster.

Further, we at shaalaa.com are providing such solutions so that students can prepare for written exams. NCERT textbook solutions can be a core help for self-study and acts as a perfect self-help guidance for students.

Concepts covered in Class 12 Chemistry chapter 4 Chemical Kinetics are Rate of a Chemical Reaction, Factors Influencing Rate of a Reaction, Half-life of a Reaction, Collision Theory of Chemical Reactions, Temperature Dependence of the Rate of a Reaction, Integrated Rate Equations - Introduction, Zero Order Reactions, First Order Reactions, Pseudo First Order Reaction, Effect of Catalyst on the Rate of Reaction, Kinetic Energy of Molecule, Role of Catalyst, Rate Law and Specific Rate Constant.

Using NCERT Class 12 solutions Chemical Kinetics exercise by students are an easy way to prepare for the exams, as they involve solutions arranged chapter-wise also page wise. The questions involved in NCERT Solutions are important questions that can be asked in the final exam. Maximum students of CBSE Class 12 prefer NCERT Textbook Solutions to score more in exam.

Get the free view of chapter 4 Chemical Kinetics Class 12 extra questions for Chemistry and can use shaalaa.com to keep it handy for your exam preparation

S