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NCERT solutions Chemistry Class 12 Part 1 chapter 4 Chemical Kinetics

Chapters

NCERT Chemistry Class 12 Part 1

Chemistry Textbook for Class 12 Part 1

Chapter 4 - Chemical Kinetics

Pages 98 - 116

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 1 | 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 2 | Page 98

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 3 | 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 4 | Page 103

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 5 | 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 6 | Page 111

What will be the effect of temperature on rate constant?

Q 7 | Page 116

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

Q 8 | 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?

Q 9 | Page 116

Pages 117 - 120

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 1.1 | 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 1.2 | 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 1.3 | 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 1.4 | 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 2 | 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 3 | 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 4 | Page 117

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

Q 5 | Page 117

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 6 | 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 8 | Page 118

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

Q 9.1 | 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 9.2 | 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 9.3 | 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 10 | 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 11 | 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 12 | Page 118

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 13 | 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 14 | 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 15 | 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 16 | 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 17 | 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 20 | 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 1.70 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 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 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 23 | 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 24 | 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 25 | Page 120

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

Calculate Ea.

Q 26 | 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 27 | 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 28 | 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 29 | 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.

Q 30 | Page 120

NCERT Chemistry Class 12 Part 1

Chemistry Textbook for Class 12 Part 1
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