Chapter-4 Chemical Kinetics

With the help of an example explain what is meant by pseudo first order
reaction.

Explain the difference between instantaneous rate of a reaction and average
rate of a reaction.

Describe how does the enthalpy of reaction remain unchanged when a catalyst
is used in the reaction.

What happens to most probable kinetic energy and the energy of activation
with increase in temperature?

All energetically effective collisions do not result in a chemical change. Explain
with the help of an example.

Match the items of Column I and Column II.
Column I                                                                   Column II
(i) Mathematical expression for rate of reaction                  (a) rate constant

(ii) Rate of reaction for zero order reaction is equal to         (b) rate law

(iii) Units of rate constant for zero order                           (c) order of
reaction is same as that of slowest step
(iv) Order of a complex reaction is                    (d) rate of a reaction
determined by

Match the items of Column I and Column II.
Column I                                                  Column II
(i) Diamond                                            (a) short interval of time
(ii) Instantaneous rate imperceptible             (b) ordinarily rate of conversion is

(iii) Average rate                                      (c) long duration of time

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

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

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

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

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

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

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

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

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

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.

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

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

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

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?

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

How can you determine the rate law of the following reaction?
2NO (g) + O2 (g) ⎯→ 2NO2 (g)

Write the rate equation for the reaction 2A + B ⎯→ C if the order of the reaction
is zero.

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

The gas phase decomposition of acetaldehyde

CH3CHO → CH4+CO Follows the rate law.

What are the units of its rate constant. 

State the order with respect to each reactant and overall reaction.

H2O + 3I- + 2H+ → 2H2O + I -

Rate = k[H2O2]1[I-]1

Give one example of pseudo first order reaction.

The conversion of molecules X to Y follows the second order of kinetics. If concentration of X is increased 3 times, how will it affect the rate of formation of Y.

The rate law for a reaction is

Rate = K [A] [B] 3/2

Can the reaction be an elementary process? Explain.

The rate of a particular reaction quadruples when the temperature changes from 293K to 313K. Calculate activation energy.

If the decomposition of nitrogen oxide as

2N2O5────> 4NO2 + O2

follows a first order kinetics.

(i)        Calculate the rate constant for a 0.05 M solution if the instantaneous rate is 1.5 x 10-6 mol/l/s?

Write the difference between order and molecularity of reaction.

Define Threshold energy and activation energy. How they are related?

The rate constant for first order reaction is 60/s. How much time will it take to reduce the concentration of the reaction to 1/10 of its initial value.

The rate of most of reaction double when their temperature is raised from

298k to 308k. Calculate the activation energy of such a reaction.

A first order reaction takes 69.3 min for 50% completion. Set up on equation for determining the time needed for 80% completion.

The decomposition of NH3 on platinum surface is a zero order reaction. What are the rate of production of N2 and H2.

If k= 2.5 x 10-4

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.

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 x 10¹⁰ s^-1. Calculate k at 318 K and E_a.

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

The rate constant for the first order decomposition of H2O2is given by the following equation:

log k = 14.34 - 1.25 x 104 K/T

Calculate Eafor this reaction and at what temperature will its half-period be 256 minutes?

The decomposition of hydrocarbon follows the equation

k = (4.5 x 1011 s-1) e-28000 K/T

Calculate Ea.

Sucrose decomposes in acid solution into glucose and fructose according to the first order rate law, witht_1/2 = 3.00 hours. What fraction of sample of sucrose remains after 8 hours?

Consider a certain reaction A → Products with k = 2.0 x 10^-2 s^-1. Calculate the concentration of A remaining after 100 s if the initial concentration of A is 1.0 mol L^-1.

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

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

Draw a graph between ln k and 1/T and calculate the values of A and E_a.

Predict the rate constant at 30 º and 50 ºC.

The following data were obtained during the first order thermal decomposition of SO₂Cl₂at a constant volume.

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

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

Calculate the rate constant.

A first order reaction takes 40 min for 30% decomposition. Calculate t_1/2.

For a first order reaction, show that time required for 99% completion is twice the time required for the completion of 90% of reaction

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.

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 1/16^thvalue?

The experimental data for decomposition of N₂O₅

in gas phase at 318K are given below:

(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)

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.

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

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:

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

2A + B → C + D

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

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

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

(i) Write the differential rate equation.

(ii) How is the rate affected on increasing the concentration of B three times?

(iii) How is the rate affected when the concentrations of both A and B are doubled?

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

(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.

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

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?

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

The decomposition of dimethyl ether leads to the formation of CH₄, H₂and 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.,

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

The decomposition of NH₃on platinum surface is zero order reaction. What are the rates of production of N₂and H₂if k = 2.5 x 10^-4mol^-1L s^-1?

For the reaction:

2A + B → A₂B

the rate = k[A][B]²with k= 2.0 x 10^-6mol^-2L²s^-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.

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

(i) 3 NO(g) → N₂O(g) Rate = k[NO]²

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

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

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

The activation energy for the reaction

2HI(g) → H2 + I2(g)

is 209.5 kJ mol-1 at 581K. Calculate the fraction of molecules of reactants having energy equal to or greater than activation energy?

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

What will be the effect of temperature on rate constant?

Time required to decompose SO₂Cl₂to half of its initial amount is 60 minutes. If the decomposition is a first order reaction, calculate the rate constant of the reaction.

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

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?

For a reaction, A + B Ã¢â€ ’Product; the rate law is given by,. What is the order of the reaction?

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

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.