1. CHEMISTRY Matter and Change
Chapter 16: Reaction Rates

2. Table Of Contents Section 16.1 A Model for Reaction Rates
CHAPTER16
Table Of Contents
Section 16.1 A Model for Reaction Rates
Section Factors Affecting Reaction Rates
Section Reaction Rate Laws
Section Instantaneous Reaction Rates and Reaction Mechanisms
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3. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Calculate average rates of chemical reactions from experimental data.
Relate rates of chemical reactions to collisions between reacting particles.
energy: the ability to do work or produce heat; it exists in two basic forms: potential energy and kinetic energy

4. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
reaction rate
collision theory
activated complex
activation energy
Collision theory is the key to understanding why some reactions are faster than others.

5. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Expressing Reaction Rates
The reaction rate of a chemical reaction is stated as the change in concentration of a reactant or product per unit of time.

6. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Expressing Reaction Rates (cont.)
Reaction rates are determined experimentally.

7. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Collision Theory
Collision theory states that atoms, ions, and molecules must collide in order to react.

8. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Collision Theory (cont.)
An activated complex is a temporary, unstable arrangement of atoms in which old bonds are breaking and new bonds are forming.

9. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Collision Theory (cont.)
The minimum amount of energy that reacting particles must have to form the activated complex and lead to a reaction is called the activation energy.
High activation energy means that few collisions have the required energy and the reaction rate is slow.

10. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Collision Theory (cont.)

11. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Collision Theory (cont.)

12. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Collision Theory (cont.)

13. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Spontaneity and Reaction Rate
Are more spontaneous reactions faster than less spontaneous reactions?
ΔG indicates only the natural tendency for a reaction to proceed—it does not affect the rate of a chemical reaction.

14. SECTION16.1
Section Check
Which of the following is NOT a requirement for a reaction to occur, according to the collision theory?
A. Reacting substances must collide.
B. Reacting substances must be in an exothermic reaction.
C. Reacting substances must collide in the correct orientation.
D. Reacting substances must collide with sufficient energy to form an activated complex.

15. SECTION16.1
Section Check
A temporary, unstable arrangement of atoms in which old bonds are breaking and new bonds are forming is called ____.
A. reaction complex
B. reaction substrate
C. activated complex
D. activated molecule

17. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Identify factors that affect the rates of chemical reactions.
concentration: a quantitative measure of the amount of solute in a given amount of solvent or solution
Explain the role of a catalyst.
catalyst
inhibitor
heterogeneous catalyst
homogeneous catalyst
Factors such as reactivity, concentration, temperature, surface area, and catalysts affect the rate of a chemical reaction.

18. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
The Nature of Reactants
Some substances react more readily than others.

19. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Concentration
Chemists change reaction rates by changing concentrations of reactants.
When concentrations are increased, more molecules are available to collide per unit volume, and therefore collisions occur more frequently.

20. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Surface Area
Greater surface area allows particles to collide with many more particles per unit of time.
For the same mass, many small particles have more surface area than one large particle.
Reaction rate increases with increasing surface area.

21. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Temperature
Increasing temperature generally increases reaction rate.
Increasing temperature increases the kinetic energy of the particles.
Reacting particles collide more frequently at higher temperatures.

22. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Temperature (cont.)
High-energy collisions are more frequent at a higher temperature.
As temperature increases, reaction rate increases.

23. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Temperature (cont.)

24. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Catalysts and Inhibitors
A catalyst is a substance that increases the rate of a chemical reaction without being consumed in the reaction.
An inhibitor is a substance that slows or prevents a reaction.

25. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Catalysts and Inhibitors (cont.)
Catalysts lower the activation energy.
Low activation energy means that more of the collisions between particles will have sufficient energy to overcome the activation energy barrier and bring about a reaction.

26. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Catalysts and Inhibitors (cont.)
A heterogeneous catalyst exists in a physical state different than that of the reaction it catalyzes.
A homogeneous catalyst exists in the same physical state as the reaction it catalyzes.

27. SECTION16.2
Section Check
Which of the following generally does not increase the rate of a chemical reaction?
A. increasing concentration
B. adding a catalyst
C. adding an inhibitor
D. increasing temperature

28. High-energy particle collisions are more frequent:
SECTION16.2
Section Check
High-energy particle collisions are more frequent:
A. when an inhibitor is present
B. when temperature is decreased
C. when activation energy is higher
D. when temperature is increased

30. SECTION16.3
Reaction Rate Laws
Express the relationship between reaction rate and concentration.
reactant: the starting substance in a chemical reaction
Determine reaction orders using the method of initial rates.
rate law
specific rate constant
reaction order
method of initial rates
The reaction rate law is an experimentally determined mathematical relationship that relates the speed of a reaction to the concentrations of the reactants.

31. Writing Reaction Rate Laws
SECTION16.3
Reaction Rate Laws
Writing Reaction Rate Laws
A rate law expresses the relationship between the rate of a chemical reaction and the concentration of the reactants.

32. Writing Reaction Rate Laws (cont.)
SECTION16.3
Reaction Rate Laws
Writing Reaction Rate Laws (cont.)
The symbol k is the specific rate constant, a numerical value that relates the reaction rate and the concentrations of reactants at a given temperature.
The specific rate constant is unique for every reaction.

33. Writing Reaction Rate Laws (cont.)
SECTION16.3
Reaction Rate Laws
Writing Reaction Rate Laws (cont.)
The reaction order for a reactant defines how the rate is affected by the concentration of that reactant.
Rate = k[H2O2]
The reaction is first order, so the rate changes in the same proportion the concentration of H2O2 changes.

34. Reaction Rate Laws 2NO(g) + 2H2(g) → N2(g) + 2H2(g)
SECTION16.3
Reaction Rate Laws
Writing Reaction Rate Laws (cont.)
2NO(g) + 2H2(g) → N2(g) + 2H2(g)
Rate = k[NO]2[H2]
If H2 is doubled, the rate doubles.
If NO is doubled, the rate quadruples because 22 = 4.
First-order H2, second-order NO, third-order overall

35. Determining Reaction Order
SECTION16.3
Reaction Rate Laws
Determining Reaction Order
The method of initial rates determines reaction order by comparing the initial rates of a reaction carried out with varying reactant concentrations.
Initial rate measures how fast the reaction proceeds at the moment when reactants are mixed.

36. Determining Reaction Order (cont.)
SECTION16.3
Reaction Rate Laws
Determining Reaction Order (cont.)

37. Determining Reaction Order (cont.)
SECTION16.3
Reaction Rate Laws
Determining Reaction Order (cont.)
Doubling [A] doubles the reaction rate, so [A] is first order.
Doubling [B] quadruples the reaction rate, so [B] is second order.
Rate = k[A][B]2

38. What is the overall reaction order of the following reaction?
SECTION16.3
Section Check
What is the overall reaction order of the following reaction?
Rate = k[A]2[B]2
A. 1st
B. 2nd
C. 3rd
D. 4th

39. SECTION16.3
Section Check
In the following reaction, what is the overall reaction order if doubling [A] results in quadrupling the reaction rate and doubling [B] results in a reaction rate eight times faster?
Rate = k[A]m[B]n
A. 12
B. 5
C. 6
D. 10

41. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Calculate instantaneous rates of chemical reactions.
Understand that many chemical reactions occur in steps.
Relate the instantaneous rate of a complex reaction to its reaction mechanism.
decomposition reaction: a chemical reaction that occurs when a single compound breaks down into two or more elements or new compounds

42. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
instantaneous rate
complex reaction
reaction mechanism
intermediate
rate-determining step
The slowest step in a sequence of steps determines the rate of the overall chemical reaction.

43. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Instantaneous Reaction Rates
This figure shows the concentration of H2O2 over time during the decomposition reaction 2H2O2(aq) → 2H2O(l) + O2(g).
The instantaneous rate is the slope of the straight line tangent to the curve at the specific time.

44. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Instantaneous Reaction Rates (cont.)
Instantaneous rate can be calculated if the concentrations are known, the temperature is known, and the experimentally determined rate law and specific rate constant at that temperature are known.
2N2O5(g) → 4NO2(g) + O2(g)
Rate = k[N2O5]
k = 1.0 × 10–5 s–1 and [N2O5] = mol/L
Rate = (1.0 × 10–5 s–1)(0.350 mol/L) = 3.5 × 10–6 mol/(L•s)

45. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Reaction Mechanisms
Most chemical reactions consist of sequences of two or more simpler reactions.
Each step is called an elementary step.
A complex reaction contains two or more elementary steps.

46. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Reaction Mechanisms (cont.)
A reaction mechanism is the complete sequence of elementary steps that makes up a complex reaction.
An intermediate is a substance produced in one of the elementary steps and consumed in a subsequent elementary step.
Intermediates do not appear in the net chemical equation.

47. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Reaction Mechanisms (cont.)
Chlorine-catalyzed decomposition of ozone

48. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Reaction Mechanisms (cont.)
Every complex reaction has one elementary step that is slower than the others.
The slowest elementary step in a complex reaction is called the rate-determining step.

49. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Reaction Mechanisms (cont.)

50. What is a reaction with two or more elementary steps called?
SECTION16.4
Section Check
What is a reaction with two or more elementary steps called?
A. compound reaction
B. complex reaction
C. multi-step reaction
D. combined reaction

51. What is the slowest step in a complex reaction called?
SECTION16.4
Section Check
What is the slowest step in a complex reaction called?
A. elementary step
B. reducing step
C. rate-determining step
D. intermediate step

53. Reaction Rates Chemistry Online Study Guide Chapter Assessment
Resources
Chemistry Online
Study Guide
Chapter Assessment
Standardized Test Practice

54. A Model for Reaction Rates
SECTION16.1
A Model for Reaction Rates
Study Guide
Key Concepts
The rate of a chemical reaction is expressed as the rate at which a reactant is consumed or the rate at which a product is formed.
Reaction rates are generally calculated and expressed in moles per liter per second (mol/(L ● s)).
In order to react, the particles in a chemical reaction must collide.
The rate of a chemical reaction is unrelated to the spontaneity of the reaction.

55. Factors Affecting Reaction Rates
SECTION16.2
Factors Affecting Reaction Rates
Study Guide
Key Concepts
Key factors that influence the rate of chemical reactions include reactivity, concentration, surface area, temperature, and catalysts.
Raising the temperature of a reaction generally increases the rate of the reaction by increasing the collision frequency and the number of collisions that form an activated complex.
Catalysts increase the rates of chemical reactions by lowering activation energies.

56. Reaction Rate Laws Key Concepts
SECTION16.3
Reaction Rate Laws
Study Guide
Key Concepts
The mathematical relationship between the rate of a chemical reaction at a given temperature and the concentrations of reactants is called the rate law.
rate = k[A] rate = k[A]m[B]n
The rate law for a chemical reaction is determined experimentally using the method of initial rates.

57. Instantaneous Reaction Rates and Reaction Mechanisms
SECTION16.4
Instantaneous Reaction Rates and Reaction Mechanisms
Study Guide
Key Concepts
The reaction mechanism of a chemical reaction must be determined experimentally.
For a complex reaction, the rate-determining step limits the instantaneous rate of the overall reaction.

58. CHAPTER16
Reaction Rates
Chapter Assessment
The energy required to initiate a reaction is called ____.
A. initiation energy
B. activation energy
C. complex energy
D. catalyst energy

59. CHAPTER16
Reaction Rates
Chapter Assessment
In general, which of the following does not cause a reaction rate to increase?
A. increasing surface area
B. increasing temperature
C. increasing volume
D. adding a catalyst

60. CHAPTER16
Reaction Rates
Chapter Assessment
What is the overall reaction order of the following reaction?
Rate = k[A][B]2[C]
A. 1st order
B. 2nd order
C. 3rd order
D. 4th order

61. CHAPTER16
Reaction Rates
Chapter Assessment
A substance produced by an elementary step in a complex reaction that is consumed later and does not show up in the net reaction is called a(n) ____.
A. activated complex
B. catalyst
C. enzyme
D. intermediate

62. CHAPTER16
Reaction Rates
Chapter Assessment
Increasing the temperature of a reaction increases the rate of reaction by:
A. increasing the collision frequency
B. increasing the number of high-energy collisions
C. both a and b
D. none of the above

63. CHAPTER16
Reaction Rates
Standardized Test Practice
Which of the following is an acceptable unit for expressing a rate?
A. mol/L ● s
B. L/s
C. M
D. mL/h

64. CHAPTER16
Reaction Rates
Standardized Test Practice
How many moles are in 4.03 × 102 g of calcium phosphate (Ca3(PO4)2)?
A moles
B moles
C moles
D moles

65. CHAPTER16
Reaction Rates
Standardized Test Practice
Doubling the concentration of one reactant in a reaction causes the reaction rate to double. What is the order of that reactant?
A. 1st
B. 2nd
C. unable to determine
D. none of the above

66. CHAPTER16
Reaction Rates
Standardized Test Practice
The rate law for the reaction A + B + C → Product is rate = k[A]2[B][C]. If [A] = 0.350M, [B] = .500M, [C] = .125M, and k = 6.50 × 10–5 L3/(mol3 ● s), what is the instantaneous rate of reaction?
A × 10–6 mol/L ● s
B × 10–7 mol/L ● s
C × 10–6 mol/L ● s
D × 10–7 mol/L ● s

67. CHAPTER16
Reaction Rates
Standardized Test Practice
H2O2 breaks down to form hydrogen and oxygen gas in what type of reaction?
A. synthesis
B. double replacement
C. decomposition
D. single replacement

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