15. Chemical Kinetics

Reaction Mechanism

Energy Diagrams, Catalysts, and Reaction Mechanisms

(b) What is the difference between a unimolecular
and a bimolecular elementary reaction?

A proposed mechanism for the oxidation of nitric oxide to 
nitrogen dioxide was described in Problem 14.29. Another 
possible mechanism for this reaction is 
2 NO1g2  k1 
k-1 
N2O21g2 Faster, reversible 
N2O21g2 + O21g2 ¡ k2 2NO21g2 Slower, rate-determining 
(c) Relate the rate constant k to the rate constants for the 
elementary reactions.

The reaction 2 NO1g2 + Cl21g2¡2 NOCl1g2 was performed
and the following data were obtained under conditions
of constant 3Cl24:
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/b13cc8f7b3c6acff-1666285465032.jpg" alt="" />
(a) Is the following mechanism consistent with the data?
NO1g2 + Cl21g2ΔNOCl21g2 1fast2
NOCl21g2 + NO1g2¡2 NOCl1g2 1slow2

Reaction Mechanism Example 2

Ozone in the upper atmosphere can be destroyed by the
following two-step mechanism:
Cl1g2 + O31g2¡ClO1g2 + O21g2
ClO1g2 + O1g2¡Cl1g2 + O21g2
(b) What
is the catalyst in the reaction?

What is the molecularity of each of the following elementary
reactions? Write the rate law for each.
(b) OCl - 1aq2 + H2O1l2¡HOCl1aq2 + OH- 1aq2

Consider the gas-phase reaction:
H2( g) + I2( g)¡2 HI( g)
The reaction was experimentally determined to be first order in
H2 and first order in I2. Consider the proposed mechanisms.
Proposed mechanism I:
H2( g) + I2( g)¡2 HI( g) Single step
Proposed mechanism II:
I2(g) Δk1k-12 I(g) Fast
H2( g) + 2 I( g) ¡k22 HI( g) Slow
b. What kind of experimental evidence might lead you to favor
mechanism II over mechanism I?

You have studied the gas-phase oxidation of HBr by O2:
4 HBr1g2 + O21g2¡2 H2O1g2 + 2 Br21g2
You find the reaction to be first order with respect to HBr
and first order with respect to O2. You propose the following
mechanism:
HBr1g2 + O21g2¡ HOOBr1g2
HOOBr1g2 + HBr1g2¡2 HOBr1g2
HOBr1g2 + HBr1g2¡ H2O1g2 + Br21g2
(a) Confirm that the elementary reactions add to give the
overall reaction.

What is the molecularity of each of the following elementary 
reactions?
(a) <img src="https://lightcat-files.s3.amazonaws.com/problem_images/66df4de62ce0b914-1672156121932.jpg" alt="" />
(b) <img src="" alt="" />
(c) <img src="" alt="" />

Reaction Mechanism Example 1

Consider the following elementary steps:NO2 (g) + NO2 (g) → NO4 (g) + NO (g) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; [SLOW] NO (g) + CO3 (g) → N (g) + CO4 (g) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; [FAST]What is the rate law of the reaction mechanism?

The gas-phase decomposition of ozone is thought to occur
by the following two-step mechanism.
Step 1: O31g2ΔO21g2 + O1g2 (fast)
(b) Derive the rate law that is consistent with this mechanism.
(Hint: The product appears in the rate law.)

The following mechanism has been proposed for the reaction
of NO with H2 to form N2O and H2O:
NO1g2 + NO1g2¡N2O21g2
N2O21g2 + H21g2¡N2O1g2 + H2O1g2
(d) The observed rate law is rate = k3NO423H24. If
the proposed mechanism is correct, what can we conclude
about the relative speeds of the first and second reactions?

The thermal decomposition of nitryl chloride, NO2Cl, is
believed to occur by the following mechanism:
NO2Cl1g2 ¡ k1 NO21g2 + Cl1g2
Cl1g2 + NO2Cl1g2 ¡ k2 NO21g2 + Cl21g2
(c) What rate law is predicted by this mechanism if the first
step is rate-determining?

Writing Rate Laws of Reaction Mechanisms Using The Rate Determining Step - Chemical Kinetics

Reaction Mechanism Concept 2

Consider this three-step mechanism for a reaction:
Cl2( g) Δk1k22 Cl( g) Fast
Cl( g) + CHCl3( g) ¡k3 HCl( g) + CCl3( g) Slow
Cl( g) + CCl3( g) ¡k4 CCl4( g) Fast
a. What is the overall reaction?

Draw a plausible transition state for the bimolecular reaction 
of nitric oxide with ozone. Use dashed lines to indicate the 
atoms that are weakly linked together in the transition state. 
NO(g) + O3(g) NO2(g) + O2(g)
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/ce6e153edc0737e6-14-49-1.jpg" alt="" />

The decomposition of hydrogen peroxide is catalyzed by
iodide ion. The catalyzed reaction is thought to proceed
by a two-step mechanism:
H2O21aq2 + I - 1aq2¡H2O1l2 + IO- 1aq2 1slow2
IO- 1aq2 + H2O21aq2¡H2O1l2 + O21g2 + I - 1aq2 1fast2
(a) Write the chemical equation for the overall process.

What is the molecularity of each of the following elementary
reactions? Write the rate law for each.
(c) NO1g2 + Cl21g2¡NOCl21g2

Reaction Mechanisms

What is the relationship between the coefficients in a balanced 
chemical equation for an overall reaction and the 
exponents in the rate law?

In a hydrocarbon solution, the gold compound
1CH323AuPH3 decomposes into ethane 1C2H62 and a
different gold compound, 1CH32AuPH3. The following
mechanism has been proposed for the decomposition of
1CH323AuPH3:
Step 1: 1CH323 AuPH3 Δ k1 k -1 1CH323Au + PH3 1fast2
Step 2: 1CH323 Au ¡k2 C2H6 + 1CH32Au 1slow2
Step 3: 1CH32Au + PH3 ¡k3 1CH32AuPH3 1fast2
(c) What is the molecularity
of each of the elementary steps?

What distinguishes the rate-determining step from the 
other steps in a reaction mechanism? How does the ratedetermining 
step affect the observed rate law?

A proposed mechanism for the oxidation of nitric oxide to 
nitrogen dioxide was described in Problem 14.29. Another 
possible mechanism for this reaction is 
2 NO1g2  k1 
k-1 
N2O21g2 Faster, reversible 
N2O21g2 + O21g2 ¡ k2 2NO21g2 Slower, rate-determining 
(a) Write a balanced equation for the overall reaction.

The rate of the reaction A + B2 S AB + B is directly proportional 
to the concentration of B2, independent of the 
concentration of A, and directly proportional to the concentration 
of a substance C. 
(c) What is the role of C in this reaction? Why doesn’t C 
appear in the chemical equation for the overall reaction?

Consider the diagram that follows, which represents two
steps in an overall reaction. The red spheres are oxygen,
the blue ones nitrogen, and the green ones fluorine. (d) Write
the rate law for the overall reaction if the first step is the
slow, rate-determining step. [Section 14.6]
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/6fdd3044e0e85a85-1666272567615.jpg" alt="" />

In a hydrocarbon solution, the gold compound
1CH323AuPH3 decomposes into ethane 1C2H62 and a
different gold compound, 1CH32AuPH3. The following
mechanism has been proposed for the decomposition of
1CH323AuPH3:
Step 1: 1CH323 AuPH3 Δ k1 k -1 1CH323Au + PH3 1fast2
Step 2: 1CH323 Au ¡k2 C2H6 + 1CH32Au 1slow2
Step 3: 1CH32Au + PH3 ¡k3 1CH32AuPH3 1fast2
(e) What is the rate law predicted by
this mechanism?

What is the molecularity of each of the following elementary
reactions? Write the rate law for each.
(a) Cl21g2¡2 Cl1g2

A proposed mechanism for the oxidation of nitric oxide to 
nitrogen dioxide was described in Problem 14.29. Another 
possible mechanism for this reaction is 
2 NO1g2  k1 
k-1 
N2O21g2 Faster, reversible 
N2O21g2 + O21g2 ¡ k2 2NO21g2 Slower, rate-determining 
(b) Show that this mechanism is consistent with the experimental 
rate law, Rate = k3NO423O24.

The following reaction of 2 Br2 (g) + 2 NO (g) → N2 (g) + 2 Br2O (g) has the following rate law:Rate = k [Br2][NO]2. The proposed mechanism for the reaction is:Br2 (g) + NO2 (g) → N (g) + Br2O (g) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;[SLOW] N (g) &nbsp;+ &nbsp;NO (g) → N2 (g) + O (g) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;[FAST] O (g) &nbsp;+ &nbsp;Br2 (g) → Br2O (g) &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;[FAST]Which of the following statements is/are false?a) The rate determining step is bimolecular. b) There are three elementary steps in the reaction mechanism. c) The mechanism possesses a catalyst. d) O is the only reaction intermediate in this reaction mechanism. e) This is not a valid mechanism for the reaction.

What is the molecularity of each of the following elementary
reactions? Write the rate law for each.

(b) H2C ¬ CH2CH21g2¡CH2“CH¬CH31g2

(b) Write the balanced reaction that corresponds to the data 
in the graph.
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/43642d15778f4d2c-1672153351677.jpg" alt="" />

Reaction Mechanism Concept 1

14.3 Reaction Mechanisms, Catalysts, and Reaction Coordinate Diagrams | General Chemistry

The decomposition of hydrogen peroxide is catalyzed by
iodide ion. The catalyzed reaction is thought to proceed
by a two-step mechanism:
H2O21aq2 + I - 1aq2¡H2O1l2 + IO- 1aq2 1slow2
IO- 1aq2 + H2O21aq2¡H2O1l2 + O21g2 + I - 1aq2 1fast2
(c) Assuming that the first step of the mechanism is rate
determining, predict the rate law for the overall process.

The following mechanism has been proposed for the gasphase
reaction of chloroform 1CHCl32 and chlorine:
Step 1: Cl21g2 Δ k1 k - 1 2 Cl1g2 1fast2
Step 2: Cl1g2 + CHCl31g2 ¡k2 HCl1g2 + CCl31g2 1slow2
Step 3: Cl1g2 + CCl31g2 ¡k3 CCl4 1fast2
(a) What is the overall reaction?

Consider the following mechanism for the reaction of 
hydrogen and iodine monochloride: 
Step 1. H21g2 + ICl1g2S HI1g2 + HCl1g2 
Step 2. HI1g2 + ICl1g2S I21g2 + HCl1g2 
(b) Identify any reaction intermediates.

Enzymes are often described as following the two-step
mechanism:
E + S Δ ES 1fast2
ES ¡ E + P 1slow2
where E = enzyme, S = substrate,
ES = enzyme9substrate complex, and P = product.
(b) Molecules that can bind
to the active site of an enzyme but are not converted into
product are called enzyme inhibitors. Write an additional
elementary step to add into the preceding mechanism to
account for the reaction of E with I, an inhibitor.

Reaction Mechanism Example 3

Consider this three-step mechanism for a reaction: 
Cl2( g) Δk1k22 Cl( g) Fast 
Cl( g) + CHCl3( g) ¡k3 HCl( g) + CCl3( g) Slow 
Cl( g) + CCl3( g) ¡k4 CCl4( g) Fast 
c. What is the predicted rate law?

Reaction Mechanism Concept 3

The addition of NO accelerates the decomposition of
N2O, possibly by the following mechanism:
NO1g2 + N2O1g2¡N21g2 + NO21g2
2 NO21g2¡2 NO1g2 + O21g2
(b) Is NO serving as a catalyst or an intermediate
in this reaction?

Consider the following energy profile.
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/02f0685dd8538c0a-1675121111211.jpg" alt="" />
(a) How many elementary reactions are in the reaction
mechanism?

What is the molecularity of each of the following elementary
reactions? Write the rate law for each.
(a) 2 NO1g2¡N2O21g2

The gas-phase decomposition of ozone is thought to occur
by the following two-step mechanism.
Step 1: O31g2ΔO21g2 + O1g2 (fast)
Step 2: O1g2 + O31g2¡2 O21g2 (slow)
(d) If instead the reaction
occurred in a single step, would the rate law change? If so,
what would it be?

Consider the reaction in which HCl adds across the double
bond of ethene:
HCl + H2C“CH2¡H3C¬CH2Cl
The following mechanism, with the accompanying energy diagram,
has been suggested for this reaction:
Step 1 HCl + H2C“CH2¡H3C“CH2+ + Cl -
Step 2 H3C“CH2+ + Cl - ¡H3C¬CH2Cl
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/53f6c6cea5140190-1660226406202.jpg" alt="" />
b. What is the expected order of the reaction based on the proposed
mechanism?

Consider this two-step mechanism for a reaction:
NO2( g) + Cl2( g) ¡k1ClNO2( g) + Cl( g) Slow
NO2( g) + Cl( g) ¡k2ClNO2( g) Fast
b. Identify the intermediates in the mechanism.

Kinetics: Chemistry's Demolition Derby - Crash Course Chemistry #32

Consider this energy diagram:
<img src="https://lightcat-files.s3.amazonaws.com/problem_images/d2c50570675bd044-1660226744911.jpg" alt="" />
a. How many elementary steps are involved in this reaction?

To answer questions 13–15, refer to the mechanism: 
H2O21aq2 + I-1aq2¡OH-1aq2 + HOI1aq2 
Slower, rate-determining 
HOI1aq2 + I-1aq2¡OH-1aq2 + I21aq2 Faster 
2 OH-1aq2 + 2 H3O+1aq2¡4 H2O1l2 Faster
Identify the catalyst and intermediate(s) in the mechanism.
(LO 14.12, 14.16)
(a) Catalyst = I-, intermediates = OH-, HOI
(b) Catalyst = H3O+, intermediate = HOI
(c) No catalyst, intermediate = I2
(d) No catalyst, intermediates = OH-, HOI

Reaction Mechanism and Molecularity Terms

Consider the reaction:
2 NH3(aq) + OCl - (aq)¡N2H4(aq) + H2O(l ) + Cl - (aq)
This three-step mechanism is proposed:
NH3(aq) + OCl - (aq) Δk1k2NH2Cl(aq) + OH- (aq) Fast
NH2Cl(aq) + NH3(aq) ¡k3N2H5+ (aq) + Cl - (aq) Slow
N2H5+ (aq) + OH- (aq) ¡k4N2H4(aq) + H2O(l ) Fast
a. Show that the mechanism sums to the overall reaction.

In Problem 14.113, you wrote a mechanism for the nitric oxide– 
facilitated decomposition of ozone. Does your mechanism 
involve a catalyst or a reaction intermediate? Explain.

Consider the following mechanism for the decomposition 
of nitramide 1NH2NO22 in aqueous solution: 
NH2NO21aq2 + OH-1aq2S NHNO2 
-1aq2 + H2O1l2 
NHNO2 
-1aq2S N2O1g2 + OH-1aq2 
(c) How will the rate of the overall reaction be affected if 
HCl is added to the solution?

The decomposition of hydrogen peroxide is catalyzed by
iodide ion. The catalyzed reaction is thought to proceed
by a two-step mechanism:
H2O21aq2 + I - 1aq2¡H2O1l2 + IO- 1aq2 1slow2
IO- 1aq2 + H2O21aq2¡H2O1l2 + O21g2 + I - 1aq2 1fast2
(b) Identify the intermediate, if any, in the mechanism.

Consider the gas-phase reaction:
H2( g) + I2( g)¡2 HI( g)
The reaction was experimentally determined to be first order in
H2 and first order in I2. Consider the proposed mechanisms.
Proposed mechanism I:
H2( g) + I2( g)¡2 HI( g) Single step
Proposed mechanism II:
I2(g) Δk1k-12 I(g) Fast
H2( g) + 2 I( g) ¡k22 HI( g) Slow
a. Show that both of the proposed mechanisms are valid.

Consider this overall reaction, which is experimentally
observed
to be second order in AB and zero order in C:
AB + C¡A + BC
Is the following mechanism valid for this reaction?
AB + AB ¡k1AB2 + A Slow
AB2 + C ¡k2AB + BC Fast

You have studied the gas-phase oxidation of HBr by O2:
4 HBr1g2 + O21g2¡2 H2O1g2 + 2 Br21g2
You find the reaction to be first order with respect to HBr
and first order with respect to O2. You propose the following
mechanism:
HBr1g2 + O21g2¡ HOOBr1g2
HOOBr1g2 + HBr1g2¡2 HOBr1g2
HOBr1g2 + HBr1g2¡ H2O1g2 + Br21g2
(b) Based on the experimentally determined
rate law, which step is rate determining?

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1. Intro to General Chemistry

2. Atoms & Elements

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4. BONUS: Lab Techniques and Procedures

5. BONUS: Mathematical Operations and Functions

6. Chemical Quantities & Aqueous Reactions

7. Gases

8. Thermochemistry

9. Quantum Mechanics

10. Periodic Properties of the Elements

11. Bonding & Molecular Structure

12. Molecular Shapes & Valence Bond Theory

13. Liquids, Solids & Intermolecular Forces

14. Solutions

16. Chemical Equilibrium

17. Acid and Base Equilibrium

18. Aqueous Equilibrium

19. Chemical Thermodynamics

20. Electrochemistry

21. Nuclear Chemistry

22. Organic Chemistry

23. Chemistry of the Nonmetals

24. Transition Metals and Coordination Compounds

[BOOK CHEM] Clutch Version

Intro to Chemical Kinetics

Chemical Kinetics is the study of factors affecting reaction rates, which examines the speed by which reactants are consumed to make products.

Average Rate of Reaction

Average (General) Rate is the change in the concentration of a compound over a period of time.

Arrhenius Equation

The Arrhenius Equation&nbsp;illustrates the temperature dependence of the rate constant k.&nbsp;

Rate Law

Rate Law represents an equation for a chemical reaction that connects the reaction rate with the concentrations or pressures of the reactants and the rate constant.&nbsp;

Factors Influencing Rates

There are 4 major factors that directly influence how fast or slow a reaction proceeds.

Stoichiometric Rate Calculations

When the rate of one compound is know, the rate of another compound is calculated through rate-to-rate comparison.

Collision Theory

According to Collision Theory:chemical reaction is successful when 2 energetic reactants successfully collide.

Integrated Rate Law

When we include the variable of time to our Rate Law then we obtain the Integrated Rate Laws.&nbsp;

Catalyst

Catalyst is a substance that increases the rate of reaction by lowering the Activation Energy (Ea) of a reaction.

Instantaneous Rate

<div title="Page 1">&nbsp;Instantaneous Rate is the rate a reaction at any particular point in time.</div>

<div title="Page 1">A Reaction Mechanism is a step-by-step sequence of elementary steps by which an overall chemical change occurs.</div>

Half-Life

Half-Life is the time it takes for half&nbsp;of a reactant to decay in a certain time period.

Energy Diagrams

Energy Diagram represents a curved plot illustrating the energies of reactants, products and transition states of a reaction.