1. Reaction Rates and Equilibrium Chapter 12 (page 366)

2. Essential Question!! What determines how rapidly chemicals will react?

3. Vocabulary: Section 1 Rate Reaction rate Molarity Stoichiometry Collision theory Activation energy Transition state Reaction profile Activated complex

4. Some reactions are fastOthers are slow C(s) + O 2 (g) → CO 2 (g)4Fe(s) + 3O 2 (g) → 2Fe 2 O 3 (s) What is a rate? How is it measured? The idea of rate

5. Why are some chemical reactions fast and some so slow? What some foods burn faster than others? What determines how fast some foods spoil? What is homeostasis and how is that similar to chemical equilibrium?

6. Average speed traveled by a typical race horse: The idea of rate

7. Beginning: High concentration of A No C present A → C At time 0 seconds

8. End: High concentration of C Low concentration of A A → C

9. Factors Affection Reaction Rates Concentration of reacting chemicals The temperature of reacting particles Surface area – size of reacting particles Addition of a catalyst or inhibitor Pressure of reactant gas or products (if gas)

10. Reaction Rate Reaction rate explains and calculates how a reaction takes place over time As the concentration of the reactants (a and b) decrease, the concentration of the concentration of products (c and d) increases (page 370) Rate = Change in Concentration = ∆ C Change in time ∆ t

11. A B 13.1 rate = -  [A] tt rate = [B][B] tt time

12. Data for Reaction of A → C Time (min) Time (sec) Moles A Moles B 001.000.00 106000.740.26 2012000.540.46 3018000.400.60 4024000.300.70

13. Sample problem Calculate the Average Rate C between 10 minutes and 20 minutes. Rate = Change in Concentration = ∆ C Change in time ∆ t = [moles of C (at 20 min) – Moles of C (at 10 min)] 20 min – 10 min = 0.2 / 10 = 0.02 moles/min

14. Assignment Take a new sheet of paper and fold it into three sections Write your name, the title of the chapter and the number On the first section from the sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

15. Practice Problems Time (min) Time (sec) Moles A Moles B 001.000.00 106000.740.26 2012000.540.46 3018000.400.60 4024000.300.70 Calculate rate of change in C between 20 minutes and 30 minutes. Calculate the rate of change in A between 1200 seconds and 1800 seconds.

16. Stoichiometry and Rate The decomposition of N 2 O 5 is shown below: 2N 2 O 5 (g) → 4NO 2 (g) + O 2 (g) The rate of decomposition of N 2 O 5 was measured after 25 seconds and found to be 5.60 x 10 -6 M/s. What is the rate of appearance of NO 2 ? Solve: 4 mol NO 2 5.06 x 10 -6 x --------------- = 1.12 x 10-5 2 mol N 2 O 5

17. Practice Problem The decomposition of KClO 3 is shown below: – 2KClO 3 → 2KCl + 3O 2, The rate of decomposition of KClO 3 was measured after 25 seconds and found to be 2.60 x 10 -3 M/s. What is the rate of appearance of O 2, ? 2KClO 3 → 2KCl + 3O 2, how many moles of oxygen are produced when 34g of KClO 3 decompose completely?

18. Collision theory Chemical reactions take place at the molecular level, where molecules of reactants are colliding with each other A + B → Products

19. Collision theory But not all collisions are successful Collision alone does not guarantee success The same is true in chemistry

20. The Collision Theory Chemical reactions take place at the level where molecules of reactants are colliding with each other (imagine a game of pool) This cannot be seen but can be observed, since reactions only take place when molecules or atoms collide with each other (very few collisions result in the actual formation of a product) In the game of pool, the balls must be hit hard enough in order for the balls to move at the right angle to go into the pocket; in reactions the right amount of energy must be achieved at the right angle, in the initial hit in order, for the bonds in the molecule of the compound to break

21. The minimum amount of energy required for a reaction to take place is referred to as the activation energy (energy of activation) E a When two molecules collide with sufficient activation energy, a new high energy state can be reached and is called the transition state The transition state is a high energy state where old bonds are broken, atoms or molecules are rearranged, and new bonds are formed (also known as the activated complex, A c ) To show what happens in a reaction, scientists show a graph that shows the progress of a reaction with respect to the energy changes that occur during a collision

22. Assignment On the second section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

23. Reaction profile Energy is released as a result of the reaction Reactants Products Reaction: A + B → C + D ∆H < 0

24. Reaction profile activation energy, E a : the minimum amount of energy required for molecules to react. Reactants Products Reaction: A + B → C + D ∆H < 0

25. A + B C + D Exothermic Reaction Endothermic Reaction The activation energy (E a ) is the minimum amount of energy required to initiate a chemical reaction. 13.4

26. Reaction profile activated complex, A c : a high- energy state where bonds are being broken and reformed; also referred to as the transition state. Reactants Products Reaction: A + B → C + D ∆H < 0

27. Reaction profile Reactants Products Reaction: A + B → C + D ∆H < 0 A c is unstable and can: proceed to C + D (products) go back to A + B (reactants) activated complex, A c

28. A catalyst is a substance that increases the rate of a chemical reaction without itself being consumed. EaEa k uncatalyzedcatalyzed rate catalyzed > rate uncatalyzed 13.6

29. C + D → A + B ∆H > 0A + B → C + D ∆H < 0 Exothermic processEndothermic process E a is larger! Exothermic reactions tend to be more common than endothermic reactions because the energy barrier is lower

30. Factors Affecting the Rate Concentration Increase or decrease in temperature Surface area of the particles involved Catalysts and inhibitors Change in volume or pressure

31. More collisions occur when the concentration of reactants is higher More collisions means more reactions are possible The reaction rate is higher when more reactants are present

32. Temperature is a measure of the average kinetic energy of molecules The higher the kinetic energy, the higher the number of molecules that successfully overcome the energy barrier Energy barrier between reactants and products Temperature

33. Increased surface area means more particles are available for collisions Increased surface area leads to a higher reaction rate AA AA AA AA AA AA AAAA More particles are exposed and available to collide with other particles to have a reaction Surface area

34. Assignment Write a three dollar summary on what has been learned in this section, be sure to use the vocabulary covered also Complete # 1 – 4 on page 404 Honors Chemistry Homework – Page 405 # 21 - 31

35. Vocabulary: Section 2 Equilibrium Dynamic Closed system Equilibrium position Le Chateliers principle Equilibrium expression Equilibrium constant Low of mass action

36. CITY traffic in traffic out There is a balance or equilibrium between cars that go into the city and cars that leave the city

37. Concept of equilibrium Physical equilibrium Chemical equilibrium Physical equilibriumChemical equilibrium There is also a “balance” in a chemical system Reactants Products N 2 (g) + 3H 2 (g) 2NH 3 (g)

38. Changes of State Equilibrium - dynamic condition in which two opposing physical or chemical changes occur at equal rates in a given closed system (constant mass ); chemical reactions are reversible When chemical equilibrium is attained, there is not net change in concentration of products and reactants – the reaction is still dynamic and not static (like a bridge connecting drivers in and out of the city; the number of people leaving the city is equal to the number going into the city) Equilibrium - does not mean that there is the same number of products and reactants, just that a balance has been reached Boiling water in a closed container is a good example of physical equilibrium, because it is an equilibrium between both phases of the same substance and the changes that take place are physical changes not chemical Even though changes cannot be seen with the naked eye (macroscopic level), changes are always dynamic on the microscopic level

40. Equilibrium and Changes of State System – anything being observed Closed system – a system with no interaction between inside and outside the reaction Open system – a system with interaction between inside and outside the reaction Phases – typical forms of matter like solids, liquids, gases, and plasma Condensation – going from gas to liquid by losing energy Concentration – how much solute is present based on the amount of solution Equilibrium position is the favored direction of a reversible reaction (and it is determined by each set of concentrations for the reactants and the products at equilibrium

41. Le Chatelier’s Principle When a physical or chemical system at equilibrium is disturbed by application of a stress (such as a change in concentration, pressure, or temperature), it attain a new equilibrium position that minimizes the stress. Scientists are constantly trying to find ways to influence the concentrations to make the reactions go in the direction that they favor Four factors that affect the direction of a reaction are: concentration, temperature, pressure and volume Anything that stresses the equilibrium (or the balance) of a reaction will cause a disturbance until a new equilibrium is reached This also applies to life, people generally avoid stress or trouble and change their behavior to adapt

42. Concept of equilibrium Physical equilibrium Chemical equilibrium Le Châtelier’s principle Effect of temperature Effect of concentration Effect of pressure / volume Chemical equilibrium Reactants Products N 2 (g) + 3H 2 (g) 2NH 3 (g) Reactants Products

43. Equilibrium Vapor Pressure of a Liquid The pressure exerted by the molecules of a vapor which are in equilibrium with its corresponding liquid at a given temperature Water can be a liquid up to 374.1 0 C See next slide

44. Physical equilibrium An equilibrium between two phases of water: H 2 O(l) H 2 O(g)

45. Equilibrium does not mean that there must be equal amounts on each side It is an equilibrium when the level of neither tank changes over time. This occurs when the amount transferred and the rate of transfer are the same from both sides Physical equilibrium 50 mL

46. Assignment On the third section of that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

47. Triple point Critical temperature

48. Critical Values Triple point- indicates the temperature and pressure at which the solid, liquid, and vapor of the substance can coexist. Critical temperature- the temperature above which the substance cannot exist in the liquid state

49. Critical Values C t water = 374.1 0 C Critical pressure - the lowest pressure required for the substance to exist as a liquid at the critical pressure. C p water = 218.3 atm

51. Le Châtelier’s principle N 2 (g) + 3H 2 (g) 2NH 3 (g) The forward reaction is favored so there is more product If an equilibrium has been established… … what happens when two NH 3 molecules are removed? You no longer have an equilibrium!The equilibrium is re-established

52. Le Châtelier’s principle: principle that states that when a “change” is made to a system at equilibrium, the system will shift in a direction that partially offsets the “change.” N 2 (g) + 3H 2 (g) 2NH 3 (g) Favored reaction If removed

53. Pressure and equilibrium Pressure or volume only affect gaseous equilibrium systems Higher pressure Smaller volume Lower pressure Larger volume The number of particles in the system is unchanged

54. 2SO 2 (g) + O 2 (g) 2SO 3 (g) 2 moles1 mole2 moles 3 moles2 moles Reactants take up more space (larger volume) than the product If we increase the pressure, the volume will decrease The equilibrium will shift to the right Pressure and equilibrium

55. 2SO 2 (g) + O 2 (g) 2SO 3 (g) 2 moles1 mole2 moles 3 moles2 moles Reactants take up more space (larger volume) than the product If we decrease the pressure, the volume will increase The equilibrium will shift to the left Pressure and equilibrium

56. The equilibrium position depends on a ratio between products and reactants, called the equilibrium expression: aA + bB cC + dD [A] means “molarity of A” raise to the power of coefficients Equilibrium constant

57. CH 4 (g) + 2H 2 S(g) CS 2 (g) + 4H 2 (g) aA + bB cC + dD Write the equilibrium expression for the following reaction: Answer: Molarities of products Molarities of reactants

58. Experimental results for: N 2 (g) + 3H 2 (g) 2NH 3 (g) at 500 o C

59. Experimental results for: N 2 (g) + 3H 2 (g) 2NH 3 (g) at 500 o C

60. Calculate the equilibrium concentration of hydrogen iodide [HI], given the following information:K = 50 at 450 o C [H 2 ] = 0.22 M, and [I 2 ] = 0.22 M H 2 (g) + I 2 (g) 2HI(g) Answer:Calculate the concentration of HI at equilibrium Given:K = 50 at 450 o C, [H 2 ] = [I 2 ] = 0.22 M Relationships:

61. Calculate the equilibrium concentration of hydrogen iodide [HI], given the following information:K = 50 at 450 o C [H 2 ] = 0.22 M, and [I 2 ] = 0.22 M H 2 (g) + I 2 (g) 2HI(g) Answer:Calculate the concentration of HI at equilibrium Given:K = 50 at 450 o C, [H 2 ] = [I 2 ] = 0.22 M Relationships: Solve: Answer:The equilibrium concentration of [HI] is 1.56 M

62. Assignment Write a three dollar summary on what has been learned in this section, be sure to use the vocabulary covered also Complete # 5 – 12 on page 404 Honors Chemistry Homework – Page 406 # 36 - 47

63. Vocabulary: Section 3 Elementary steps Reaction mechanism Intermedialt Unimolecular Bimolecular Rate determining step

64. reaction mechanism: a proposed sequence of elementary steps that leads to product formation. Most reaction mechanisms must be determined using experimental evidence.

65. elementary steps: a series of simple reactions that represent the overall progress of the chemical reaction at the molecular level. H 2 (g) + 2ICl(g) → I 2 (g) + 2HCl(g) Consider the following reaction: The proposed reaction mechanism that is supported by experimental evidence is: Elementary step 1: H 2 + ICl → HI + HCl Elementary step 2: HI + ICl → I 2 + HCl

66. Notice that HI gets canceled out because it appears once on the reactant side, and once on the product side H 2 (g) + 2ICl(g) → I 2 (g) + 2HCl(g) Consider the following reaction: The proposed reaction mechanism that is supported by experimental evidence is: Elementary step 1: H 2 + ICl → HI + HCl Elementary step 2: HI + ICl → I 2 + HCl Overall reaction: H 2 + 2ICl → I 2 + 2HCl Add the elementary steps Two-step reaction mechanism

67. H 2 (g) + 2ICl(g) → I 2 (g) + 2HCl(g) Consider the following reaction: The proposed reaction mechanism that is supported by experimental evidence is: Elementary step 1: H 2 + ICl → HI + HCl Elementary step 2: HI + ICl → I 2 + HCl Overall reaction: H 2 + 2ICl → I 2 + 2HCl Add the elementary steps Two-step reaction mechanism

68. intermediate: a chemical species that is formed during the elementary steps, but is not present in the overall balanced equation. H 2 (g) + 2ICl(g) → I 2 (g) + 2HCl(g) Consider the following reaction: HI is a reaction intermediate! Two-step reaction mechanism

69. H 2 (g) + 2ICl(g) → I 2 (g) + 2HCl(g) Consider the following reaction: The reaction can’t occur in one step! The likelihood of three molecules colliding at just the right orientation and speed is just about zero. Two-step reaction mechanism

70. Some reactions have more than 2 elementary steps. Elementary step 1: Elementary step 2: Elementary step 3: Overall reaction: NO 2 (g) + F 2 (g) NO 2 F 2 (g) F(g) + NO 2 (g) 2NO 2 (g) + F 2 (g) →→→→→→ NO 2 F 2 (g) NO 2 F(g) + F(g) NO 2 F(g) 2NO 2 F(g) Two intermediates: NO 2 F 2 (g) and F(g)

71. Some reactions have more than 2 elementary steps. Elementary step 1: Elementary step 2: Elementary step 3: Overall reaction: NO 2 (g) + F 2 (g) NO 2 F 2 (g) F(g) + NO 2 (g) 2NO 2 (g) + F 2 (g) →→→→→→ NO 2 F 2 (g) NO 2 F(g) + F(g) NO 2 F(g) 2NO 2 F(g) 1 reactant that decomposes: This elementary step is unimolecular Molecularity

72. Some reactions have more than 2 elementary steps. Elementary step 1: Elementary step 2: Elementary step 3: Overall reaction: NO 2 (g) + F 2 (g) NO 2 F 2 (g) F(g) + NO 2 (g) 2NO 2 (g) + F 2 (g) →→→→→→ NO 2 F 2 (g) NO 2 F(g) + F(g) NO 2 F(g) 2NO 2 F(g) 2 reactants colliding: This elementary step is bimolecular Molecularity

73. Assignment On the first section of the back side from that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

74. Some reactions have more than 2 elementary steps. Elementary step 1: Elementary step 2: Elementary step 3: Overall reaction: NO 2 (g) + F 2 (g) NO 2 F 2 (g) F(g) + NO 2 (g) 2NO 2 (g) + F 2 (g) →→→→→→ NO 2 F 2 (g) NO 2 F(g) + F(g) NO 2 F(g) 2NO 2 F(g) (fast) (slow) (fast) Remember: Some chemical reactions are fast, others are slow Each elementary step takes place at a different rate Reaction rates

75. Some reactions have more than 2 elementary steps. Elementary step 1: Elementary step 2: Elementary step 3: Overall reaction: NO 2 (g) + F 2 (g) NO 2 F 2 (g) F(g) + NO 2 (g) 2NO 2 (g) + F 2 (g) →→→→→→ NO 2 F 2 (g) NO 2 F(g) + F(g) NO 2 F(g) 2NO 2 F(g) (fast) (slow) (fast) The overall reaction can only proceed as fast as the slowest elementary step Reaction rates

76. Some reactions have more than 2 elementary steps. Elementary step 1: Elementary step 2: Elementary step 3: Overall reaction: NO 2 (g) + F 2 (g) NO 2 F 2 (g) F(g) + NO 2 (g) 2NO 2 (g) + F 2 (g) →→→→→→ NO 2 F 2 (g) NO 2 F(g) + F(g) NO 2 F(g) 2NO 2 F(g) (fast) (slow) (fast) rate determining step: the slowest elementary step in the reaction mechanism that determines the overall rate (or speed) of the chemical reaction.

77. Remember: an activated complex is highly unstable, and only exists for a fraction of a second; an intermediate is more stable. 2 elementary steps (2 peaks) The intermediate becomes a reactant for the second step

78. How many elementary steps are there in this overall reaction?

79. 1 2 3 4 There are 4 elementary steps

80. How many intermediates are formed? 1 2 3 4 There are 4 elementary steps

81. How many elementary steps are there in this overall reaction? There are 3 intermediates 1 2 3 4 1 2 3 There are 4 elementary steps

82. Assignment On the second section of the back side from that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

83. Biological pathways C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2 + energy (2 ATP) glucose (sugar)ethanolcarbon dioxideenergy Yeasts use alcoholic fermentation to produce energy:

84. Biological pathways C 6 H 12 O 6 → 2C 2 H 5 OH + 2CO 2 + energy (2 ATP) glucose (sugar)ethanolcarbon dioxideenergy Yeasts use alcoholic fermentation to produce energy: This process contains a large number of steps Breakdown of glucose via fermentation requires 12 enzymes! Biological substances that help speed up chemical reactions

85. Reaction mechanisms are proposed based on experimental evidence A series of elementary steps make up the overall reaction The slowest elementary step is the rate determining step for the overall reaction

86. Assignment Write a three dollar summary on what has been learned in this section, be sure to use the vocabulary covered also Complete # 13 – 18 on page 404 Honors Chemistry Homework – Page 405 # 48 - 52

87. Vocabulary: Section 4 Catalyst Enzymes

88. Reaction profile activation energy, E a : the minimum amount of energy required for molecules to react. Reactants Products Reaction: A + B → C + D ∆H < 0 If E a is very high, the reaction might take place very slowly or not take place at all

89. Reaction: A + B → C + D ∆H < 0 Catalysts are substances that lower the energy barrier Catalysts are not consumed during the reaction and can be reused

90. catalyst: a substance that speeds up the rate of a chemical reaction by providing a pathway with a lower activation energy. Reaction: A + B → C + D ∆H < 0 Catalysts work by providing a new pathway with a lower activation energy Biological catalysts are called enzymes

91. Enzymes H 2 O(l) + CO 2 (g) → H + (aq) + HCO 3– (aq) Carbonic anhydrase (enzyme) Carbonic anhydrase helps to remove CO 2 from your tissues by dissolving it in the form of HCO 3–. Saliva contains carbonic anhydrase. The tingling sensation comes from the acid H + when it touches the nerve endings on your tongue

92. Enzymes Gelatin is a protein made from collagen The gelatin is able to hold its shape The gelatin never polymerizes (“sets”) when pineapple is added… Why?

93. Enzymes Gelatin is a protein made from collagen Pineapple contains an enzyme called bromelain, that helps “break down” protein Without the bonds responsible for protein structure, the protein in gelatin cannot hold together. The gelatin never polymerizes (“sets”) when pineapple is added…

94. Catalysts and the environment Ozone (O 3 ) protects us from harmful radiation from the sun. The natural ozone cycle (in the stratosphere) occurs as follows: O 3 (g) + UV(radiation) → O + O 2 (g) O + O 2 (g) → O 3 (g) How O 3 is replenished What happens when chlorofluorocarbons (CFCs) are present? Freon–11Freon–12 used in air conditioning systems, aerosols and in the manufacture of Styrofoam™products

95. O 3 (g) + UV(radiation) → O + O 2 (g) O + O 2 (g) → O 3 (g) How O 3 is replenished Natural ozone cycle: Ozone depletion mechanism: Cl(g) + O 3 (g) → ClO(g) + O 2 (g) O + ClO(g) → Cl + O 2 (g) O + O 3 (g) → 2O 2 (g) Step 1: Step 2: Overall: O 3 is not replenished ClO is an intermediate Cl is not consumed; it is a catalyst. Catalysts and the environment

96. Assignment On the third section of the back side from that sheet of paper, please write six things that you learned from your notes so far that could appear on your test.

97. Freon–11Freon–12 used in air conditioning systems, aerosols and in the manufacture of Styrofoam™products Ozone depletion mechanism: Cl(g) + O 3 (g) → ClO(g) + O 2 (g) O + ClO(g) → Cl + O 2 (g) O + O 3 (g) → 2O 2 (g) Step 1: Step 2: Overall: O 3 is not replenished In 1996, the manufacture of freon was banned with a 10-year grace period for developing countries Catalysts and the environment

98. Catalysts are important Catalysts are important because: Without catalysts, the only way to speed up a reaction is by raising the temperature, which is not always possible or safe Society depends on the high speed production of chemicals used for food, shelter and clothing Environmental chemists can use catalysts to reduce the amount of high- level pollutants; Los Angeles was the first city to mandate the use of catalytic converters on cars Living organisms (including humans) would not exist without enzymes

99. Reaction: A + B → C + D ∆H < 0 Catalysts are substances that lower the energy barrier Catalysts are not consumed during the reaction and can be reused Biological catalysts are called enzymes

100. Test: - Next week Tuesday or Thursday depending on your class. Homework requirement: Learn all terms and concepts covered on this topic. Make sure you have all assignments between page 404 and 407 completed and turned in by your test date.