Kinetics of Homogeneous Processes. Individual assignments

The Ministry of education and science of the Russian Federation Federal state budget educational

institution of higher education

«Kazan National Research Technological University»

KINETICS OF HOMOGENEOUS

PROCESSES

Individual assignments

Kazan

KNRTU Publishing house 2016

UDK 66.061.1.012.7

BBK 35.115

O. N. Kadkin [et al.]; The Ministry of education and science of the Russian Federation, Kazan National Research Technological University. – Kazan : KNRTU Publishing house, 2016. – 28 p.

The present individual assignments for student's self-guidance work in the discipline "Physical Chemistry" contain theoretical questions and problems.

The present materials were designed for providing the students with new information and testing them on the topic "Chemical Kinetics". They can be used to carry out the seminars and practical trainings for students of technological specialities.

The manual is developed at the department of physical and colloid chemistry.

The manual is approved for publication by the decision of the educational methodology commission of the institute of polymers

Reviewers: Ph.D. in Chemistry, Associate Professor of Department of CTHMWC N. N. Nikitina

Ph.D. in Chemistry, Associate Professor of Department of CTONC T. N. Sobachkina

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SECTION I. THE BASIC CONCEPTS AND LAWS OF

CHEMICAL KINETICS

Assignment 1

1.How do you understand the term "the rate of a chemical reaction"? What are the factors on which it depends?

2.What is the dimension of the reaction rate constant, k, for a zero-order reaction?

3.What experimental data are necessary for determining the reaction kinetic order?

4.Deduce an equation for the half-life, τ1/2, of a second-order reaction for the case when the initial concentration of reactants are equal.

5.Derive the expression for the reaction rate constant, k, of gas-phase reactions of the general type, A B + C, using the values of the initial (pо) and total (p) pressure in the system.

6.The volume, V, of oxygen that evolves upon decomposition of N2O5 in CCl4 in varies with time as follows:

Calculate the reaction rate constant and show using the graphical method that this is a first-order reaction.

Assignment 2

1.Formulate the basic postulate of chemical kinetics.

2.Write down the mathematical expression for the true rate of the reaction, А В.

3.What methods of determination of the reaction order are related to the group of integral methods?

4.Illustrate graphically the dependence of the reaction rate constant on the concentration of reactants.

5.How to explain that the reaction,

30C2H5OH + B10H14 10B(OC2H5)3 + 22H2,

is of the 2nd order but not of the 31st order? Write the kinetic equation for the given example.

6.During catalytic decay of ammonia to simple substances on the wolfram wire at Т=1100°C, the time required for decomposition of half of all the

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amount of NH3 depends on the initial pressure of ammonia as follows:

Determine the order of the reaction and its kinetic constant.

Assignment 3

1.Explain the physical meaning of the reaction rate constant. On which parameters does it depend?

2.Can the reaction order be fractional?

3.What kind of a graphical dependence does a kinetic curve show?

4.The data on changes in the concentration of a reactant with time are obtained upon studying the reaction kinetics. Which method of determination of the reaction order is most efficient in this case?

5.An irreversible reaction of which order, first-, second-, or third-order, will proceed faster under the condition of equal initial concentrations and equal kinetic constants?

6.The kinetic constant of the reaction,

,

is following: k = 2.2 × 10–4 s–1. Determine the initial concentration of isobutylene, if its concentration after 3600 s from the reaction start became equal to 1.0 × 10–4 mol/L.

Assignment 4

1.What is called the order of a chemical reaction? For what type of reactions the order and molecularity always coincide?

2.What methods can be used for determination of the reaction rate?

3.Specify the unit of the rate constant for the 1st order reactions.

4.Illustrate schematically kinetic curves with respect to the concentration of a starting reactant for irreversible reactions of the first and second orders in the same diagram.

5.Compare the reaction rate constants for two first-order reactions in the case, when the half life of the first reaction is by 5 times larger than of the second one.

6.During the reaction,

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Cu + (NH4)2S2O8 = CuSO4 + (NH4)2SO4,

the concentration of CuSO4 in different periods of time varied as follows:

The initial concentration of (NH4)S2O8 was 0.219 mol/L. Determine the order and rate constant of the reaction.

Assignment 5

1.What does the term "half-life of a reaction" mean? Can it be applied to secondand third-order reactions?

2.What is the difference between the order and molecularity of a chemical reaction?

3.Describe the method of equal concentrations and the isolation method for experimental determination of the reaction order.

4.Illustrate schematically the dependence graph, which can be used for determination of the rate constant of a third-order reaction at equal concentrations of starting reagents.

5.The following kinetic equation was obtained for the reaction,

What is the overall reaction order? Make some assumptions about the mechanism of this chemical reaction.

6.The amount of the reacted compound in the rearrangement reaction of cyclohexenylallylmalononitrile at 135°C in different periods of time have been changed as follows:

Determine the reaction rate constant using the graphical method.

Assignment 6

1.Explain the term "molecularity of a chemical reaction". Can the molecularity be greater or smaller than the reaction order?

2.Specify the unit for the rate constant of a second-order reaction.

3. What is the relationship between the half-life of a reaction and the

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initial concentration of a starting reagent in the case of 2-nd and 3-rd order reactions?

4.Upon studying the kinetics of a chemical reaction, the kinetic curves with different concentrations of reagents have been obtained. Which of the methods of determination of the reaction order is most effective in this case?

5.The reaction, 2HCrO4–+3HSO3– + 5H+ 2Cr3+ + 3SO42– +5H2O, is described by the following kinetic equation:

w = k[HCrO4–][3HSO3–]2[H+].

Why is the rate of this reaction not proportional to the number of ions of each sort in accordance with the stoichiometric coefficients in the chemical equation?

6.The conversion of benzoyl peroxide into diethyl ether (1st order reaction) at 60°С proceeds by 75.2% in 10 minutes. Calculate the reaction rate constant.

Assignment 7

1.What are called the reaction order with respect to one of the individual reactants and the overall kinetic order of a reaction?

2.Can the numerical values of rate constants be compared with each other for reactions of different orders?

3.What experimental data are necessary for determining the reaction order?

4.Show graphically the general character of the time dependence of the concentration of a final product for a zero-order reaction.

5.Write down and integrate the kinetic equation of the reaction, the order of which equals 1/2. Deduce the expression for the half-life of this reaction.

6.The concentration of NH3 upon its decomposition in different periods of time have been changed as follows:

Determine the reaction order and the reaction rate constant.

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Assignment 8

1.Give the expression for the rate of the irreversible reaction, the mechanism of which is described by the chemical equation,

2А + В С.

2.Specify the unit for the rate constant of a third-order reaction.

3.Can one determine the order of a chemical reaction, knowing stoichiometric coefficients in the chemical equation of this reaction?

4.What experimental data do reveal the influence of intermediate compounds and final products on the reaction rate?

5.Find the expression for the half-life, τ1/2, of a third-order reaction for the case when the initial concentrations of starting reagents are equal.

6.The concentrations of HCN and С3H7СНО in the reaction between propionic aldehyde and hydrocyanic acid (aqueous solution at 25о) in different periods of time terms have been changed as follows:

The initial concentrations of НСN and С3H7СНО were 0.1 and 0.06 mol/L, respectively. Determine the reaction order and calculate the reaction rate constant.

Assignment 9

1.In which cases is the reaction rate defined as the change in the concentration of reactants per unit time?

2.Can the molecularity and reaction order be fractional values?

3.How to demonstrate that a particular reaction is of the first order?

4.What information about a chemical reaction can you get from the time dependence of the concentration of a reactant?

5.The experimentally established kinetic equation for the reaction,

2NO + O2 2NO2, can be expressed as follows:

Can one make the following conclusions: а) The reaction is trimolecular.

b) The reaction proceeds in one stage.

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c)The overall reaction order is 3.

d)The reaction is of the first order with respect to NO and O2.

7.The concentration of BrO– in the reaction, ClO– + Br– BrO– + Cl–, has been changed in different periods of time as follows:

The concentrations of NaClO and KBr in the reaction mixture at τ = 0 equaled 0.00323 and 0.002508 mol/L, respectively. Determine the reaction order and calculate the rate constant?

Assignment 10

2.How does the half-life of a first-order reaction depend on the concentration of reactants?

3.Which methods of determination of the reaction order are related to the group of differential methods?

4.If the order of the reaction, А + В С, is determined under the

condition, СА = СВ, then which of the order values, the order with respect to an individual reactant or the overall reaction order, is obtained using such an approach?

5.Get the expression for the rate constant of a gas-phase reaction of the general type, А В + С + D, using the values of the initial (p0) and current (p) pressure of gases in the system.

6.The rate constant of the second-order reaction,

СН3СООС2Н5 + NaOH CH3COONa + C2H5OH,

is 5.4 L/(mol × min). The initial concentrations of ester and alkali were 0.04 and 0.02 mol/L, respectively. Find the amount of ester consumed within 10 min after the reaction start.

Assignment 11

1.Write down the expression for the rate constant of a second-order reaction at unequal concentration of starting reagents.

2.How can the rate of a chemical reaction be determined experimentally?

3. If the method of flooding (Oswaldʹs isolation method) is used for

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determination of the reaction order, then which type of the reaction orders, the overall order or the order with respect to one of the reactants, is determined with applying such an approach?

4.In which coordinates should the kinetic diagram be drawn in order to get a linear dependence of the function of concentration on time for a first-order reaction?

5.For the reaction, I– + OСl– Cl– + OI–, the following kinetic equation is derived experimentally: w = k [I–] [OСl–]. What is the total reaction order? Give explanation of your answer. Suggest a mechanism for this reaction.

6.In the reaction of isomerization of ethylene dichloride,

,

the concentration of trans-isomer in different periods of time varied as follows:

What is the order of the reaction? What amount of time does the isomerization of the half-quantity of trans-isomer require?

Assignment 12

1.What is understood under the term "molecularity of a chemical reaction"? To what kind of reactions is this concept applicable?

2.If k = 0.3 L/(mol min), then what is the reaction order? Express k in cm3/(mol s).

3.In what kind of reactions the concentration of a reactant linearly decreases with time?

4.Illustrate schematically the kinetic curve for the change of the concentration of the substance, B, in the following irreversible chemical reaction: A B.

5.For the reaction Br– + OСl– Cl– + OBr–, the following kinetic equation is derived experimentally: w = k [Br–] [OСl–]. What is the total reaction order? Give explanation of your answer. Suggest a mechanism for this reaction.

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6.In the reaction, 2Сe4+ + As3+ 2Ce3+ + As4+, the concentration of Ce4+ in different periods of time varied as follows:

Determine the order of the reaction and its kinetic constant.

Assignment 13

1.How is the basic postulate of chemical kinetics formulated?

2.Can numerical values of the rate constants for reactions of different orders be compared with each other?

3.What experimental data point to the influence of intermediate substances and final products on the reaction rate?

4.The order of the reaction, А + В + С D, was determined under the condition, СА0 СА0 СА0. Which kind of the reaction order, the order with respect to a particular reactant or the total reaction order, is determined in this case?

5.Show graphically the dependence of the concentration of a reaction product on time for the case of a second-order reaction.

6.For the reaction, 2Ce4+ + As3+ 2Ce3+ + As4+, determine the order of the

reaction and its kinetic constant using the following experimental data on the equal concentrations of Ce4+ and As3+.

Assignment 14

1.In which cases the reaction rate is defined as the change in concentration of reactants per unit time?

2.How does the concentration of a reaction product change over the course of a first-order reaction?

3.How does the half-life of a first-order reaction depend on the initial concentration of a reactant?

4.Upon studying the kinetics of a reaction, a series of values of the changes in the concentration of a reactant in time is obtained. What method of determination of the reaction order is most efficient in this case?

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