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Presentation on theme: "Term Test 2 Click Here. This presentation is completely interactive In order for this presentation to work you MUST follow the indicated tabs on each."— Presentation transcript:

1 Term Test 2 Click Here

2 This presentation is completely interactive In order for this presentation to work you MUST follow the indicated tabs on each slide Answer the question on a separate piece of paper and compare with the slides This presentations purpose is diagnose what you havent understood or what you havent attempted Follow it properly and you will succeed! Next Slide

3 Factors Affecting the Rates of Chemical Reactions Next Slide When Chemists study reactions, they have observed many factors that increase or decrease the over all concentration per unit time. These changes have allowed for advancements in chemical research, specifically in Chemical Kinetics.

4 Factors Affecting the Rate of Chemical Reactions Next Slide By definition, CHEMICAL KINETICS is the study of chemical reactions, specifically looking at the quantitative (numerical/mathematical) study of reaction rates. A REACTION RATE (sometimes referred to as the speed of a reaction) is the change of concentration of reactants or products per unit time. In other words, it is how fast or slow a reaction takes place. It is important to understand that reaction rates allow chemists to differ between slow reactions, like the oxidation of iron into rust, and fast reactions, like the combustion of fire works.

5 Factors Affecting the Rate of Chemical Reactions Next Slide

6 Factors Affecting the Rate of Chemical Reactions Next Slide The Second Factor which affects the Rate of Chemical Reactions is the CONCENTRATION of the REACTANTS during a reaction. HIGHER CONCENTRATION, implies that more molecules will be available for interaction with other molecules, thus increasing the rate. LOWER CONCENTRATION, implies that less molecules will interact with each other, thus decreasing the rate. In the video, you see a difference in the concentration of coal particles. Obviously, on the left, there arent as many particles compared to the right. Thus it is right to say that the flame on the right is burning more coal than the flame on the left. Thus the rate of the flame on the right is greater because more coal is being burned for the same unit time.

7 Factors Affecting the Rate of Chemical Reactions Next Slide The Third Factor which affects the Rate of Chemical Reactions is the TEMPERATURE in which the reaction takes place. HIGHER TEMPERATURE, implies that molecules will be moving quicker and will interact more often, increasing the likeability that the molecules will interact properly, speeding up the rate of reaction. LOWER TEMPERATURE, implies that molecules will be moving slower, decreasing the likeability that molecules will interact properly, slowing down the rate of reaction.

8 Factors Affecting the Rate of Chemical Reactions Next Slide The Fourth Factor which effects the Rate of Chemical Reactions is CATALYSTS. A catalyst is meant to speed up a reaction while decreasing the activation energy of a reaction. It is important to note that a catalyst in a reaction will be produced in the reaction, otherwise it is not a catalyst! In biology, ENZYMES are the catalyst of frequent topic because it allows our body to undergo reaction with minimal energy requirements in a efficient manner. In the video you see the dissociation of hydrogen peroxide into water and oxygen with the help of the catalyst manganese dioxide which remains constant in system. The presence of the catalyst increases the rate of reaction which normally would be extremely slow.

9 Factors Affecting the Rate of Chemical Reactions Next Slide The Fifth and Final Factor which effects the Rate of Reaction is the PHYSICAL STATE OF THE REACTANTS. The physical state of reactants can largely effect the rate of a reaction because it effects whether or not a sufficient amount of reactants can react. Suppose you are trying to burn a log of wood, the combustion of the organic compound will only react on the surface, because the center of the log isnt it contact with oxygen and fire which is required for this reaction. Thus, the SURFACE AREA of reactants will effect the rate of reaction. Also, a compound in AQUEOUS form allows for movement of the compound in a reaction. Thus, if reactants are dissolved in solution, the rate of reaction will increase.

10 Answer QUESTION 1 Chemical Kinetics is the __________ study of reaction _________. a)Qualitative, Rates b)Quantitative, Rates c)Qualitative, Processes d)Quantitative, Processes Factors Affecting the Rate of Chemical Reactions

11 Next Question QUESTION 1 ANSWER Chemical Kinetics is the QUANTITATIVE study of reaction RATES. a)Qualitative, Rates b)Quantitative, Rates c)Qualitative, Processes d)Quantitative, Processes Factors Affecting the Rate of Chemical Reactions Next Section

12 Answer QUESTION 2 (Pulled from winter midterm 2011) Which of the following statements is false? A. The rate of a reaction usually increases when the concentration of one of the reactants is increased. B. The rate of a reaction is dependent on temperature. C. The rate of a reaction may be increased by certain catalytic agents. D. A reaction will proceed rapidly if the activation energy is large. E. The rate of a reaction describes the change in concentration of a reactant or product with time. Factors Affecting the Rate of Chemical Reactions

13 Next Question Factors Affecting the Rate of Chemical Reactions Next Section QUESTION 2 ANSWER Which of the following statements is false? A. The rate of a reaction usually increases when the concentration of one of the reactants is increased. B. The rate of a reaction is dependent on temperature. C. The rate of a reaction may be increased by certain catalytic agents. D. A reaction will proceed rapidly if the activation energy is large. E. The rate of a reaction describes the change in concentration of a reactant or product with time.

14 Answer QUESTION 3 Which one of the following reactions reacts the most rapidly at room temperature. A) 2 H 2 + O 2 2 H 2 O B) H + + OH - H 2 O (neutralization) C) C 12 H 22 O 11 (sugar) 12 C + 11 H 2 O D) 4Fe + 3O 2 2Fe 2 O 3 Factors Affecting the Rate of Chemical Reactions

15 Next Question Factors Affecting the Rate of Chemical Reactions Next Section QUESTION 3 ANSWER Which one of the following reactions reacts the most rapidly at room temperature. A) 2 H 2 + O 2 2 H 2 O B) H + + OH - H 2 O (neutralization) C) C 12 H 22 O 11 (sugar) 12 C + 11 H 2 O D) 4Fe + 3O 2 2Fe 2 O 3 *** IONS REACT THE QUICKEST!

16 Answer QUESTION 4 (pulled from the University of Waterloo Chemical Kinetics website) Which one of the following burns easily and why? A) a bar of steel B) steel sheet C) steel wool D) steel pipe Factors Affecting the Rate of Chemical Reactions

17 Next Question Factors Affecting the Rate of Chemical Reactions Next Section QUESTION 4 ANSWER Which one of the following burns easily and why? A) a bar of steel B) steel sheet C) steel wool D) steel pipe *** Surface Area is greatly increased and allows for the steel to burn.

18 Answer QUESTION 5 Glycolysis, an energy pathway in both anaerobic and aerobic bodies, is undergone in organisms. What is the greatest factor that allows this reaction to occur? A) Catalyst B) Temperature C) Nature of Reactants D) Physical State of Reactants E) Reactant Concentration Factors Affecting the Rate of Chemical Reactions

19 Next Section QUESTION 5 ANSWER Glycolysis, an energy pathway in both anaerobic and aerobic bodies, is the process of breaking done Glucose into products in organisms. What is the most likely factor that allows this reaction to occur? A) Catalyst B) Temperature C) Nature of Reactants D) Physical State of Reactants E) Reactant Concentration The activation energy of glucose is decreased in every intermediate step and allows for minimal amounts of energy to be used by organisms to break the molecule because organisms do not have the capabilities to combust this sugar.

20 Average and Instantaneous Rates of Change Next Slide Because the rate of reaction is defined as being the change in concentration over the change in time, it is proper practice to discuss average and instantaneous rates of change.

21 Average and Instantaneous Rates of Change Next Slide An AVERAGE RATE of change is quantified by the following equation: This equation allows us to determine the Average Rate when given information in a chart and if given information in a graph. Graphically, the average rate of change is the slope of a line between two points often referred to as the secant. t (in s) [A]

22 Average and Instantaneous Rates of Change Next Slide An INSTANTANEOUS RATE of change is quantified by the following equation: This equation allows us to determine the Instantaneous Rate when given a single concentration at a moment of time. Graphically, the instantaneous rate of change is the tangent of a point. t (in s) [A]

23 Average and Instantaneous Rates of Change Next Slide Because the Rate of Reaction can be determined for any reactant or product in a reaction, there must be a way to differ between Reactants and Products. We will define the RATE OF CONSUMPTION to be the rate of which the reactants are used. We will define the RATE OF PRODUCTION to be the rate of which the products are used.

24 Answer QUESTION 6 What is the Average Rate of Change for the following equation given the following chart of data? a.Between 10 and 0 for oxygen gas b.Between 20 and 30 for Glucose (sugar) Average and Instantaneous Rates of Change

25 Next Question QUESTION 6 ANSWER What is the Average Rate of Change for the following equation given the following chart of data? a.Between 10 and 0 for oxygen gas b.Between 20 and 30 for Glucose (sugar) Average and Instantaneous Rates of Change Next Section

26 Answer QUESTION 8 What is the Rate of Production of Carbon dioxide given the following data? a)From 0 seconds to 10 seconds b)From 20 seconds to 30 seconds Average and Instantaneous Rates of Change

27 Next Question QUESTION 8 ANSWER What is the Rate of Production of Carbon dioxide given the following data? a)From 0 seconds to 10 seconds b)From 20 seconds to 30 seconds Average and Instantaneous Rates of Change Next Section

28 Answer QUESTION 9 (Pulled from winter midterm 2011) Sucrose is fermented to ethanol and carbon dioxide in the following reaction. C 12 H 22 O 11(aq) + H 2 O (l) 4 CH 3 CH 2 OH (aq) + 4 CO 2(g) If the rate of production of CO 2 is mol/Ls, then what is the rate of consumption of C 12 H 22 O 11 ? A)1.00 mol/Ls B) 6.25×102 mol/Ls C) mol/Ls D) 4.00 mol/Ls E) mol/Ls Average and Instantaneous Rates of Change

29 Next Section QUESTION 9 ANSWER Sucrose is fermented to ethanol and carbon dioxide in the following reaction. C 12 H 22 O 11(aq) + H 2 O (l) 4 CH 3 CH 2 OH (aq) + 4 CO 2(g) If the rate of production of CO 2 is mol/Ls, then what is the rate of consumption of C 12 H 22 O 11 ? A)1.00 mol/Ls B) 6.25×102 mol/Ls C) mol/Ls D) 4.00 mol/Ls E) mol/Ls *** you must make the mols equivalent in order to find the answer. Average and Instantaneous Rates of Change

30 Rate laws for Chemical Reactions Next Slide In Chemical Kinetics, we can determine a RATE LAW which is the quantitative relation between the reaction rate and the concentrations of the reactants. This will prove to be useful in determining new properties for Chemical Kinetics.

31 Rate Laws for Chemical Reactions Next Slide As explained in the previous slide, a RATE LAW is the quantitative relation between the reaction rate and the concentrations of the reactants. A Rate Law has the following form for the following reaction: Where k is the RATE CONSTANT and x and y are the ORDERS of the reaction in respect to their compounds. In other words, x is the order of the reaction in respect to methane and y is the order of the reaction in respect to oxygen. *** RATE is always in mol/Ls, thus, the rate constant (k) will have different units for different orders.

32 Rate Laws for Chemical Reactions Next Slide Suppose the following reaction was undergone: If we wanted to determine the RATE LAW for the following reaction, we would need to obtain data experimentally. This data would include concentrations of all reactants and the INITIAL RATE of these reactants. The initial rate is the instantaneous rate of change for a reaction at time equal to zero. Suppose this data was obtained for the following reaction and was put in the following chart: How can we determine the proper rate law given this information? The method of Initial Rates!

33 Rate Laws for Chemical Reactions Next Slide Data From Previous Slide STEP 1Assume the rate law for the given reaction STEP 2Look for concentrations that remained constant among experiments. STEP 3Create equations for the following experiments and solve for order. Thus the appropriate RATE LAW is

34 Rate Laws for Chemical Reactions Next Slide Data From Previous Slide It is now time to determine the value of the rate constant. In order to do this, we must choose any values from a single experiment and solve for k.

35 Answer QUESTION 10 Given the following Chemical Equations, Determine the Generic Rate law for each: 1) 2) 3) Rate Laws for Chemical Reactions

36 Next Question QUESTION 10 ANSWER 1) 2) 3) Rate Laws for Chemical Reactions Next Section

37 Answer QUESTION 11 During a chemical reaction, three compounds are combined simultaneously. Calculations are made and the order of reactant A and B are determined. If the order of reactant A is 2 and the order of reactant B is 0, what is the order of reactant C assuming the units on the rate constant are: Rate Laws for Chemical Reactions

38 Next Question QUESTION 11 ANSWER Thus the order of reactant C is 3 Rate Laws for Chemical Reactions Next Section

39 Answer QUESTION 12 (pulled from midterm) A reaction, A + B products, was studied using the method of initial rates. The initial rate of consumption of B was measured in three different experiments. Data are provided below: What are the correct units for the rate constants, k for this reaction? Rate Laws for Chemical Reactions

40 Continue QUESTION 12 ANSWER *** We must first determine the order. STEP 1Assume the rate law for the given reaction STEP 2Look for concentrations that remained constant among experiments. STEP 3Create equations for the following experiments and solve for order. Thus the appropriate RATE LAW is Rate Laws for Chemical Reactions

41 Next Section QUESTION 12 ANSWER *** Now that we have the proper Rate Law, we can use it to determine the units on k. *** Thus the answer is C. Rate Laws for Chemical Reactions

42 Integrated Rate Laws Next Slide Because Rate is equivalent to a differential expression, it is often the case that an integrated form of the Rate Law can be achieved which allows Chemists to use these equations for different types of calculations.

43 Integrate Rate Law Next Slide The Equations achieved by integration of Rate Laws are as follows (These can be found on your Data Sheet): Zero-Order Reactions First-Order Reactions Second-Order Reactions

44 Answer QUESTION 13 The chemical equation describing the decomposition of Dinitrogen Pentoxide is: The reaction is first-order and the rate constant is k =.0682 min ¹. If 1.00 mol of dinitrogen pentoxide is placed in a 2.00L reaction vessel at 352 C, then how long will it take for 25% of the dinitrogen pentoxide to react? Integrate Rate Law

45 Next Section QUESTION 13 ANSWER *** 25% used means 75% remains *** Thus it will take 4.21 minutes. Integrate Rate Law

46 Analysis of Concentration vs. Time Data Next Slide When dealing with Orders of reactions, there is often two approaches used to determine the order when data is given in respect to concentration and time. These methods are the Graphical and Algebraic methods.

47 Analysis of Concentration vs. Time Data Next Slide For each of the three orders that are discussed in this course, there is an equation derived from its integrated equation. This equation is simply solving for the rate constant and is useful when given data because for one of the orders we should expect the rate constant to remain constant.

48 Analysis of Concentration vs. Time Data Next Slide The Graphical Approach allows one to determine the order simply by looking at the Graph. All you need to do is remember a few rules and you should be fine at solving these types of problems. For ZERO ORDER reactions, you should expect to see a NEGATIVE linear slope with a plot of [A] vs. t For FIRST ORDER reactions, you should expect to see a NEGATIVE linear slope with a plot of ln[A] vs. t For SECOND ORDER reactions, you should expect to see a POSITIVE linear slope with a plot of 1/[A] vs. t

49 Answer QUESTION 14 Determine the order of the following reaction (using both the graphical and algebraic method) given the following data: Analysis of Concentration vs. Time Data

50 Next Section QUESTION 14 ANSWER Algebraic Method Graphical Method *** Thus this reaction must be of order 2! Analysis of Concentration vs. Time Data

51 Half-Life Next Slide Half-life, is a period of time it takes for a substance to decay to half of it original value. Obviously, because this is a change in the amount of a substance for a given time, this can easily be related to Rate of Reactions in Chemical Kinetics.

52 Half- Life Next Slide In this course, we can achieve half-life formulae for each of the orders we discuss. The derivation can be found in the course-notes: ZERO ORDER FIRST ORDER SECOND ORDER

53 Answer QUESTION 15 A ancient rock is found on the coast of western Canada. This rock seems to have deposits of Uranium, a nuclear decaying element, assuming that the following reaction is a first order reaction. How old is this rock if 15.7% of Uranium is present (assuming that the amount of uranium originally on the rock was known) and the half-life of Uranium is years? Half-Life

54 Next Section QUESTION 15 ANSWER First, we must determine the value of k using the half-life formula for a first- order reaction: Second, we must use the integrated first-order formula to calculate time t when only 15.7% remains. Thus, the rock should be approximately years old! Half-Life

55 Reaction Mechanisms Next Slide The topics of Chemical Kinetics usually involve REACTION MECHANISMS which consist of elementary processes that occur in a specific order summing up to an overall reaction. These mechanisms all have separate rates and thus are extremely important to study! A great animation of Reaction Mechanisms can be found at n3/reactionmechanisms.htm

56 Reaction Mechanisms Next Slide The best way to understand a REACTION MECHANISM is to look at an example. The following is the reaction mechanism between 2-bromo-2-methylpropane and a hydroxide ion: (CH ) C is an example of an INTERMEDIATE. An intermediate can appear in the mechanism but will not appear in the reaction. When you sum up the ELEMENTARY PROCESSES, you achieve the overall reaction, which is what we are most comfortable with!

57 Reaction Mechanisms Next Slide As stated earlier, ELEMENTARY PROCESSES are the most simplistic processes usually involving a specific collision or a molecular process. The following are just a few of the rate laws for elementary processes: *** These rules only apply to Elementary Processes! First-Order (Unimolecular) Second-Order (Bimolecular) Third-Order (Termolecular)

58 Reaction Mechanisms Next Slide Two Cases to consider when determining the Rate Law from a Mechanism: 1)Are the speeds of the reactions known? Is there a distinctive slow reaction? If a slow reaction is determined we can simply determine the Rate Law according to that step because it is known that the Overall Rate is approximately equal to the Rate of the slowest step! 2) If the speeds of the reaction arent given we must do much math. We must pick a random step and determine the Rate Law for that step and combine them with all other intermediate steps.

59 Reaction Mechanisms Next Slide While solving these problems, we will encounter a case where we will have intermediates that must be removed from the Rate Law. In order to do this, we must use the STEADY STATE APPROXIMATION. This allows us to exchange the rate of producing an intermediate with the rate of consuming an intermediate (and vice versa). Think of the steady state as a limit, the production of an intermediate is high at the beginning of a reaction because the concentration of the reactants are high. Once this concentration of the intermediate increases, so does the consumption of the intermediate. But once the concentration of the initial reactants decreases so does that speed of the production of the intermediate which eventually will hit a steady state (a constant value) where the production and consumption of the intermediate is approximately equivalent. In the later reaction, the consumption begins to get larger than the production depending on the speed of the mechanisms.

60 Answer QUESTION 16 TRUE/FALSE A Rate Law for a specific reaction allows one to determine the order for each reactant in a reaction and also the how reactants are actually converted into products. Reaction Mechanisms

61 Next Question QUESTION 16 ANSWER FALSE The overall reaction does not tell us how a reactant is converted into a product, it is a sum of everything that has occurred. An elementary process will depict the actual conversion of a reactant into a product. Reaction Mechanisms Next Section

62 Answer QUESTION 17 An Elementary Process is an event that depicts a __________ or ___________. A)Molecular Process, Reaction Order B)Collisional Event, Reaction Order C)Molecular Process, Reaction Speed D) Molecular Process, Collisional Event E) Reaction Order, Reaction Speed F) Reaction Speed, Collisional Event Reaction Mechanisms

63 Next Question QUESTION 17 ANSWER An Elementary Process is an event that depicts a MOLECULAR PROCESS or COLLISIONAL EVENT. A)Molecular Process, Reaction Order B)Collisional Event, Reaction Order C)Molecular Process, Reaction Speed D) Molecular Process, Collisional Event E) Reaction Order, Reaction Speed F) Reaction Speed, Collisional Event Reaction Mechanisms Next Section *** Reaction Order can be determined from an elementary process but an elementary process does not determine the Reaction Order. *** Reaction Speed is a property of molecules present in a elementary process.

64 Answer QUESTION 18 It is understood that the rate of an elementary process is proportional to the total collision rate which is proportional to the concentration of the reactants. An elementary process is also proportional to the fraction of collisions with sufficient kinetic energy and the fraction of collisions with correct alignment. Which of the following statements are true according to this information. 1) (Initially) 2) (for a non-zero ordered reaction) 3) If the concentration of the Reactants were to increase, the Order of the Elementary Process would be altered. 4) If the concentration of the Reactants were to increase, the Initial Rate of an Elementary Process would increase. Reaction Mechanisms

65 Next Question QUESTION 18 ANSWER 1)FALSE *** concentrations of one reactant has no effect on the concentration of another initially, once a reaction proceeds. this would be true because of steady state. 2)TRUE 3)TRUE 4)TRUE Reaction Mechanisms Next Section

66 Answer QUESTION 19 Nitrogen monoxide reacts with hydrogen gas to produce nitrogen gas and water vapour. The mechanism is believed to be: Step 1: 2 NO N 2 O 2 Step 2: N 2 O 2 + H 2 N 2 O + H 2 O Step 3: N 2 O + H 2 N 2 + H 2 O What is the overall balanced equation and any reaction intermediates? Reaction Mechanisms

67 Next Question QUESTION 19 ANSWER To find the overall balanced equation, cross out substances that appear in equal numbers on both sides of the reaction and add together like items on the same side of the equation: Step 1: 2 NO N 2 O 2 Step 2: N 2 O 2 + H 2 N 2 O + H 2 O Step 3: N 2 O + H 2 N 2 + H 2 O Net Reaction: 2 NO + 2 H 2 N H 2 O To identify the reaction intermediates, look for substances that first appear on the product side of the equation, but then appear in the next step as a reactant. Intermediates: N 2 O 2 and N 2 O. Reaction Mechanisms Next Section

68 Answer QUESTION 20 Determine the Rate of Reaction for the following reaction mechanism: Overall Reaction: 2 NO 2 + F 2 2NO 2 F Step 1: NO 2 + F 2 NO 2 F + F (slow) Step 2: NO 2 + F NO 2 F (fast) Reaction Mechanisms

69 Next Question QUESTION 20 ANSWER Overall Reaction: 2 NO 2 + F 2 2NO 2 F Step 1: NO 2 + F 2 NO 2 F + F (slow) Step 2: NO 2 + F NO 2 F (fast) Rate = K[NO 2 ][F 2 ] *** Since no intermediates are present in the rate determining step, it is simply the rate law for that step. To determine the rate law, you must apply the same laws for elementary processes. Reaction Mechanisms Next Section The slowest step of any mechanism is often referred to as the RATE DETERMINING STEP because the rate law can be derived from that step!

70 Answer QUESTION 21 Determine the Rate of Reaction for the following reaction mechanism: Overall Reaction: H 2 + Br 2 2HBr Step 1: Br 2 2Br (fast) Step 2:Br + H 2 HBr + H (slow) Step 3:H + Br HBr (fast) Reaction Mechanisms

71 Next Section QUESTION 21 ANSWER Overall Reaction: H 2 + Br 2 2HBr Step 1: Br 2 2Br (fast) Step 2:Br + H 2 HBr + H (slow) Step 3:H + Br HBr (fast) In this problem an intermediate exists, Because of that, it is a two step problem. First, we will determine the Rate of the slowest step: Then we will determine the rate of any intermediates in our initial rate: ****** Reaction Mechanisms The slowest step of any mechanism is often referred to as the RATE DETERMINING STEP because the rate law can be derived from that step!

72 How Does Temperature Affect Reaction Rate? Next Slide As we discussed earlier, Temperature has a large effect on the rate of chemical reactions. It is usually the case that increasing temperature will result in a faster rate of reaction. In this section we will discuss the affects of temperature and get into some Collision Theory.

73 How Does Temperature Affect Reaction Rate? Next Slide By definition, TEMPERATURE is the average measure of KINETIC ENRGY or molecules in a system. From Question 18, we briefly discussed the proportionalities of Rate: it is observed that rate is proportional to three important factors: 1)The frequency of collision (How often collision take place). 2)The number of collision that are properly aligned over the total number of collisions. 3)The number of collision that have enough kinetic energy for the reaction to undergo over the total number of collisions. The third point is very important when talking about temperature because we know that if we increase temperature, which will increase the average kinetic energy in a system, we will expect the number of collisions that have enough kinetic energy to produce a proper change to increase because there is more kinetic energy in the system. Thus, this is why when temperature is increased, rate is also increased.

74 How Does Temperature Affect Reaction Rate? Next Slide When a collision is undergone, it is important to note that there is often an activated complex associated with each collision for all molecules. The ACTIVATED COMPLEX is the short-lived, high-energy complex in a chemical reaction that persists while old bonds are breaking and new bonds are forming. This activated complex deals with the conversion of kinetic energy from the reaction to potential energy in the complex. *** It is important to note that an activated complex will be formed whether or not a sufficient amount of kinetic energy is present. BUT, if the kinetic energy for a given collision isnt greater than or equal to the forward activation energy, the activated complex will be converted back into reactant form.

75 How Does Temperature Affect Reaction Rate? Next Slide There are two activation energies associated for a reaction. The first is the FORWARD activation energy, which would be the activation energy seen on the left of the potential energy diagram, and the second is the REVERSE activation energy, which would be seen on the right of the potential energy diagram. The relationship between these two energies can be quantified by the following equation which includes the enthalpy of the reaction (the change in energy between products and reactants).

76 How Does Temperature Affect Reaction Rate? Next Slide Svante Arrhenius was the first to quantify a constant k for the three proportionalities of Rate. His efforts have been quantified in the following equation similar to the Clausius-Cloperon equation. This Arrhenius equation dictates a relationship of the activation energy for a reaction which is said to be determined by the slope of the plot of ln(k) versus (1/T).

77 Answer QUESTION 22 The Activation Complex is a ____________, ______________ complex that is formed when the ____________ energy of the collisions has been converted into the ___________ energy stored within complex. 1)Potential 2)Low-energy 3)Short-lived 4)Kinetic 5)Long-lived 6)High-energy *** Determine the list of numbers, in order, that will satisfy the following definition of the Activated Complex. Reaction Mechanisms

78 Next Question QUESTION 22 ANSWER The Activation Complex is a Short-lived, High-energy complex that is formed when the Kinetic energy of the collisions has been converted into the Potential energy stored within complex. 1)Potential 2)Low-energy 3)Short-lived 4)Kinetic 5)Long-lived 6)High-energy ***(3, 6, 4, 1) How Does Temperature Affect Reaction Rate? Next Section

79 Answer QUESTION 23 For a specific reaction, the forward activation energy is KJ/mol and the reverse activation energy J/mol. Determine the enthalpy of this reaction and dictate whether it is endothermic or exothermic. How Does Temperature Affect Reaction Rate?

80 Next Question QUESTION 23 ANSWER Since the enthalpy for this reaction is positive, this reaction is ENDOTHERMIC. How Does Temperature Affect Reaction Rate? Next Section

81 Answer QUESTION 24 Consider the following Data: k = T = 286K k = T = 354K Determine the activation energy from this data by the Arrhenius Equation. How Does Temperature Affect Reaction Rate?

82 Next Section QUESTION 24 ANSWER Thus the Activation Energy is 9.4 KJ/mol How Does Temperature Affect Reaction Rate?

83 Catalysts Next Slide As discussed earlier, a Catalyst is very important in a reaction because it lowers the activation energy of a reaction. In biology, this is extremely important because without these necessity molecules, our bodies wouldnt be able to function properly and life as we know it would be completely different.

84 Catalysts Next Slide During a reaction, a catalyst is usually noted when it starts as a reactant and is produced as a product. Thus, a major role in determining the presence of a catalyst is to show that it isnt used up in a reaction, it must remain present in the overall reaction. Though the mechanism of a reaction involving a catalyst may show the use of the catalyst, it must in the end reproduce the catalyst. A major calculation involving catalysts is to show how much faster the reaction is with or without the catalyst.

85 Catalysts Next Slide As the course notes state, DO NOT ASSUME THE RATE- DETERMINING STEP IS THE STEP WITH THE HIGHEST ACTIATION ENERGY!!! The rate determining step is always the elementary process that has the transition state of highest energy! That is, given a potential energy diagram, the step that has the highest amount of potential energy, is the step that is the rate determining step! Rate-Determining Step

86 Answer QUESTION 25 Determine how many intermediates are in the following Potential energy diagram and also determine the Rate-Determining Step: Reaction Mechanisms

87 Next Question QUESTION 25 ANSWER Reaction Mechanisms Thus there are 3 intermediates… Dont get confused with activated complexes! Rate Determining Step

88 Answer QUESTION 26 Given the following reactions, which ones contain a catalyst? 1)2) Step 1: 2 NO N 2 O 2 Step 2: N 2 O 2 + H 2 N 2 O + H 2 O Step 3: N 2 O + H 2 N 2 + H 2 O 3)4) Reaction Mechanisms

89 Next Question QUESTION 26 ANSWER 1) No Catalysts present 2) No Catalysts present 3) Catalyst present 4) Catalyst present Reaction Mechanisms

90 Answer QUESTION 27 A catalyst decreases the activation energy of a given reaction by exactly 17 kJ/mol. By what factor does the reaction rate increase at 25 o C when the catalyst is used? Assume that the Arrhenius pre-exponential factor, A, is the same for the catalyzed and uncatalyzed reactions. Reaction Mechanisms

91 START OVER QUESTION 27 ANSWER First, lets suppose the uncatalyzed activation energy is x, thus the catalyzed activation energy is x-17. Reaction Mechanisms


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