NCERT Solutions for Class 12 Chemistry Chapter 4 - Chemical Kinetics

Question 1:

From the concentration of C₄H₉Cl (butyl chloride) at different times given below, calculate the average rate of reaction:

Question 2:

Ammonia and oxygen react at high temperature as:
4NH₃(g) + 5O₂(g) ¾→ 4NO(g) + 6H₂O (g)
In an experiment, rate of formation of NO is 3.6 × 10^–3 mol L^–1s^–1. Calculate (i) rate of disappearance of ammonia, (ii) rate of formation of water.

Question 3:

Calculate the overall order of a reaction, which has the rate expression :
(i) Rate = k [A]^1/2 [B]^3/2 (ii) Rate = k [A]^3/2 [B]^–1

Question 4:

Identify the reaction order from each of the following rate constants.

1. k = 2.3 × 10^–5 L mol^–1 s^–1
2. k = 3.2 × 10^–4 s^–1

Question 5:

The decomposition of N2O5 at 318 K according to the following equation follows first order reaction :

The initial concentration of N2O5 was 1.24 × 10–2 mol L–1 and that after 60 minutes was 0.20 × 10–2 mol L–1. Calculate the rate constant of the reaction at 318 K.

Question 6:

The following data were obtained during the first order thermal decomposition of N2O5(g) at constant volume,

Calculate the rate constant.

Question 7:

A first order reaction is found to have a rate constant, k = 5.5 × 10^–14 s^–1. Find the half life period of the reaction.

Question 8:

Show that in case of a first order reaction, the time taken for completion of 99.9% reaction is ten times the time required for half change of the reaction.

Question 9:

The rate constant of a reaction at 500K and 700 K are 0.02 s^–1 and 0.07 s^–1 respectively. Calculate the values of Ea and A.

Question 10:

The first order rate constant for the decomposition of ethyl iodide by the reaction:
C₂H₅I(g) $\to$ C₂H₄ (g) + HI (g)
at 600 K is 1.60 × 10–5 s^–1. Its energy of activation is 209 kJ mol–1. Calculate the rate constant of the reaction at 700 K.

Question 11:

In a reaction 2A $\to$ 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 time interval.

Question 12:

For a reaction, A + B $\to$ Product, the rate is given by,
r = k[A]^1/2[B]².
What is the order of the reaction ?

Question 13:

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

Question 14:

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

Question 15:

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.

Question 16:

What will be the effect of temperature on rate constant ?

Question 17:

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

Question 18:

The activation energy for the reaction
2HI (g) $\to$ H₂(g) + I₂(g)
is 209.5 kJ mol^–1 at 581 K. Calculate the fraction of molecules of reactants having energy equal to or greater than activation energy.

Question 19:

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

Question 20:

For the reaction :
2A + B $\to$ 2AB
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.

Question 21:

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

Question 22:

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

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

Question 23:

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

Question 24:

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 ?

Question 25:

What is the effect of temperature on the rate constant of reaction ? How can this temperature effect on rate constant be represented quantitatively ?

Question 26:

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

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

Question 27:

A reaction is first order in A and second order in B.

1. Write the differential rate equation
2. How is the rate affected on increasing the concentration of B three times ?
3. How is the rate affected when the concentrations of both A and B are doubled ?

Question 28:

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 :

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

Question 29:

The following results have been obtained during the kinetic studies of the reaction :
2A + B $\to$ C + D

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

Question 30:

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 :

Question 31:

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

Question 32:

The half-life for radioactive decay of¹⁴C is 5730 years. An archaeological artifact contained wood had only 80% of the ¹⁴C found in a living trees. Estimate the age of the sample.

Question 33:

The experimental data for decom-position of N2O5
2N2O5 $\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$$\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$ $\to$ 4NO2 + O2
in gas phase at 318K are given below :

1. Plot [N2O5] against t.
2. Find the half-life period for the reaction.
3. Draw a graph between log [N2O5] and t.
4. What is the rate law ?
5. Calculate the rate constant.
6. Calculate the half-life period from k and compare it with (b).

Question 34:

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 ?

Question 35:

During nuclear explosion, one of the products is ⁹⁰Sr with half-life of 28.1 years. If 1 $\mathrm{\mu }$g 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?

Question 36:

Show that time required for 99% completion is twice the time required for the completion of 90% reaction.

Question 37:

A first order reaction takes 40 min for 30% decomposition. Calculate t^1/2.

Question 38:

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

Question 39:

The following data were obtained during the first order thermal decomposition of SO2Cl2 at a constant volume.

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

Question 40:

The rate constant for the decomposition of hydrocarbons is 2.148 × 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?

Question 41:

Consider a certain reaction A $\to$ Products with k = 2.0 × 10^–2s^–1. Calculate the concentration of A remaining after 100 s if the initial concentration of A is 1.0 mol L^–1.

Question 42:

Sucrose decomposes in acid solution into glucose and fructose according to the first order rate law, with t_1/2 = 3.00 hours. What fraction of sample of sucrose remains after 8 hours?

Question 43:

The decomposition of hydrocarbon follows the equation k = (4.5 × 10¹¹s^–1)e^–28000K/T. Calculate Ea.

Question 44:

The rate constant for the first order decomposition of H₂O₂ is given by the following equation :
log k = 14.34 – 1.25 × 10⁴K/T
Calculate Ea for this reaction and at what temperature will its half-period be 256 minutes?

Question 45:

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

Question 46:

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 A is 4 × 10¹⁰s^–1, calculate k at 318 K and E_a.

Question 47:

The rate of 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.

Question 48:

State a condition under which a bimolecular reaction is kinetically first order reaction.

Question 49:

Write the rate equation for the reaction
2A + B $\to$ C if the order of the reaction is zero.

Question 50:

How can you determine the rate law of the following reaction?
2NO(g) + O₂(g) $\to$ 2NO₂ (g)

Question 51:

For which type of reactions, order and molecularity have the same value?

Question 52:

In a reaction if the concentration of reactant A is tripled, the rate of reaction becomes twenty seven times. What is the order of the reaction?

Question 53:

Derive an expression to calculate time required for completion of zero order reaction.

Question 54:

For a reaction A + B $\to$ Products, the rate law is : Rate = k[A][B]^3/2.
Can the reaction be an elementary reaction? Explain.

Question 55:

For a certain reaction large fraction of molecules has energy more than the threshold energy, yet the rate of reaction is very slow. Why?

Question 56:

For a zero order reaction will the molecularity be equal to zero? Explain.

Question 57:

For a general reaction A $\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$$\raisebox{1ex}{$3$}\!\left/ \!\raisebox{-1ex}{$4$}\right.$$\to$ B, plot of concentration of A vs time is given in figure below. Answer the following question on the basis of this graph.

1. What is the order of the reaction?
2. What is the slope of the curve?
3. What are the units of rate constant?

Question 58:

The reaction between H₂(g) and O₂(g) is highly feasible yet allowing the gases to stand at room temperature in the same vessel does not lead to the formation of water. Explain.

Question 59:

Why does the rate of a reaction increase with rise in temperature?

Question 60:

Oxygen is available in plenty in air yet fuels do not burn by themselves at room temperature. Explain.

Question 61:

Why is the probability of reaction with molecularity higher than three very rare?

Question 62:

Why does the rate of any reaction generally decreases during the course of the reaction?

Question 63:

Thermodynamic feasibility of the reaction alone cannot decide the rate of the reaction. Explain with the help of one example.

Question 64:

Why in the redox titration of KMnO₄ vs oxalic acid, we heat oxalic acid solution before starting the titration?

Question 65:

Why can’t molecularity of any reaction be equal to zero?

Question 66:

Why molecularity is applicable only for elementary reactions and order is applicable for elementary as well as complex reactions?

Question 67:

Why can we not determine the order of a reaction by taking into consideration the balanced chemical equation?