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Entry Task: Dec 6 th Thursday Question : For the general rate law, Rate = k[A] [B] 2, what will happen to the rate of reaction if the concentration of.

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Presentation on theme: "Entry Task: Dec 6 th Thursday Question : For the general rate law, Rate = k[A] [B] 2, what will happen to the rate of reaction if the concentration of."— Presentation transcript:

1 Entry Task: Dec 6 th Thursday Question : For the general rate law, Rate = k[A] [B] 2, what will happen to the rate of reaction if the concentration of A is tripled? You have 5 minutes!

2 Agenda: Go through the answers to Rate Law ws #1 Walkthrough NOTES Ch. 14 sec 3 – The change in concentration with time (integrated – graph) Rate Law ws #2

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4 1. For 2 A + B C, weve determined the following experimental data: a. Rate order for A is _____and B is______ b. The rate law for this reaction is: c. The overall reaction order is_______. d. Provide the rate constant for this reaction 12 Rate = k[A] 1 [B] x10 -5 = k[0.0100] 1 [0.0100] x10 -5 = k= 16.2 M -1 s x10 -6

5 2. For 2 A + B C, weve determined the following experimental data: a. Rate order for A is _____and B is______ b. The rate law for this reaction is: c. The overall reaction order is_______. d. Provide the rate constant for this reaction 21 Rate = k[A] 2 [B] x10 -3 = k[0.026] 2 [0.015] x10 -3 = k= 277 M -1 s x10 -5

6 3. The following data were measured for the reaction of nitric oxide with hydrogen:2 NO(g) + 2 H 2 (g) N 2 (g) + 2 H 2 O(g) Using these data, determine (a) the rate law for the reaction, (b) the rate constant, (c) the rate of the reaction when [NO] = M and [H 2 ] = M.

7 3. Using these data, determine (a) the rate law for the reaction Exp. 1 vs. Exp. 2, we doubled the concentration of H 2, the rate doubled as well. This means [H 2 ] 1

8 3. Using these data, determine (a) the rate law for the reaction Exp. 1 vs. Exp. 2, we doubled the concentration of H 2, the rate doubled as well. This means [H 2 ] 1 Exp. 2 vs. Exp. 3, we doubled the concentration of NO and the rate quadrupled or 2 2. This means that NO is 2 nd order [NO] 2 a) Rate = k[NO] 2 [H 2 ] 1

9 3. Using these data, determine (a) the rate law for the reaction, (b) the rate constant, c) the rate of the reaction when [NO] = M and [H 2 ] = M. a) Rate = k[NO] 2 [H 2 ] 1 k= Rate [NO] 2 [H 2 ] 1 = 4.92 x M/s [0.20] 2 [0.10] 1 = 1.2 M -2 /s -1

10 3. Using these data, determine (a) the rate law for the reaction, (b) the rate constant, (c) the rate of the reaction when [NO] = M and [H 2 ] = M. a) Rate = k[NO] 2 [H 2 ] 1 b) k = 1.2 M 1 s 1 Rate = (1.2 M 1 s 1 ) (0.050 M) 2 (0.150) Rate = 4.5 x M/s

11 The following data were collected for the rate of disappearance of NO in the reaction: 2NO (g) + O 2 (g) 2NO 2 (g) Experiment[NO] (M)[O 2 ] (M)Initial Rate M/s x x x a) What is the rate law for the reaction? For [NO], if you doubled the concentration, the rate goes up by a factor of 4 so [NO] 2 For [O 2 ], if you doubled the concentration, the rate doubles so [O 2 ] 1

12 The following data were collected for the rate of disappearance of NO in the reaction: 2NO (g) + O 2 (g) 2NO 2 (g) Experiment[NO] (M)[O 2 ] (M)Initial Rate M/s x x x c) What is the average value of the rate constant calculated from the three data sets. SHOW YOUR WORK!! k= Rate [NO] 2 [H 2 ] 1 = 5.64 x M/s [0.0252] 2 [0.125] 1 = 7.11x10 3 M -2 /s -1

13 Consider the gas-phase reaction between nitric acid oxide ad bromine at 273°C: 2NO (g) + Br 2 (g) 2NOBr (g) Experiment[NO] (M)[Br 2 ] (M)Initial Rate M/s a) Determine the rate law? For [NO], if you doubled the concentration, the rate goes up by a factor of 4 so [NO] 2 For [Br 2 ], if you doubled the concentration, the rate doubles so [Br 2 ]

14 14.23 Consider the gas-phase reaction between nitric acid oxide ad bromine at 273°C: 2NO (g) + Br 2 (g) 2NOBr (g) Experiment[NO] (M)[Br 2 ] (M)Initial Rate M/s b) Calculate the average value of the rate constant for the appearance of NOBr from our four data sets. k= Rate [NO] 2 [Br 2 ] 1 = 150 M/s [0.25] 2 [0.20] 1 = 1.2 x10 4 M -2 /s -1

15 Consider the gas-phase reaction between nitric acid oxide ad bromine at 273°C: 2NO (g) + Br 2 (g) 2NOBr (g) Experiment[NO] (M)[Br 2 ] (M)Initial Rate M/s c) How is the rate of appearance of NOBr related to the rate of disappearance of Br 2 ? Rate = 1111 [Br 2 ] t = 1212 [NOBr] t

16 Consider the gas-phase reaction between nitric acid oxide ad bromine at 273°C: 2NO (g) + Br 2 (g) 2NOBr (g) Experiment[NO] (M)[Br 2 ] (M)Initial Rate M/s d) What is the rate of disappearance of Br 2 when [NO] = 0.075M and [Br 2 ] = M? = k Rate [NO] 2 [Br 2 ] 1 [0.075] 2 [0.185] 1 = 2(1.2 x10 4 M -2 /s -1 ) = 6.1 M/s

17 Chemical Kinetics I can… Graph the relationship of time with amount of reactant concentrations and integrate this with rates of reactions. Determine the graphical relationship between time and the rate order.

18 Chemical Kinetics Equation Sheet Under thermochemistry and kinetics 1 st order 2 nd order Arrhenius Equation

19 Chemical Kinetics Chapter 14 section 3 Notes

20 Chemical Kinetics Two Types of Rate Laws 1.Differential- Data table contains RATE AND CONCENTRATION DATA. Uses table logic or algebra to find the order of reaction and rate law 2.Integrated- Data table contains TIME AND CONCENTRATION DATA. Uses graphical methods to determine the order of the given reactant. K=slope of best fit line found through linear regressions

21 Chemical Kinetics Integrated Rate Law Can be used when we want to know how long a reaction has to proceed to reach a predetermined concentration of some reagent

22 Chemical Kinetics Graphing Integrated Rate Law Time is always on x axis Plot concentration on y axis of 1 st graph Plot ln [A] on the y axis of the second graph Plot 1/[A] on the y axis of third graph You are in search of a linear graph

23 Chemical Kinetics Zero order Reactions- Use A B as an example. What happens when we double [A], what happens to the rate of reaction that is zero order? So does the concentration affect rate? Y/N____ What would the rate law be for a zero order? The rate of reaction does not change No Rate = k

24 Chemical Kinetics Sketch a graph with rate on Y and concentration on X axis- Label axis!! As concentration increases, the rate of reaction remains the same.

25 Chemical Kinetics Sketch a graph with concentration on Y and time on X axis- Label axis!! Integrated Rate laws We look for straight lines. This provides a clean visual about the relationship of concentration and time.

26 Chemical Kinetics Sketch a graph with concentration on Y and time on X axis- Label axis!! So when we plot our data table and get a negative straight line it is ____________order! Slope is negative (-k)

27 Chemical Kinetics First Order Reactions A B in a reaction. Write the rate expression for reactant A. (sec. 1stuff) Rate = - [A] t

28 Chemical Kinetics The Change of Concentration with Time Write the rate law for reactant A. (sec 2 stuff) Rate = k[A] 1

29 Chemical Kinetics The Change of Concentration with Time Describe a First Order reaction. Double the concentration the reaction doubles. Low amount of reactant = low rate of reaction

30 Chemical Kinetics Sketch a graph with rate on Y and concentration on X axis- Label axis!! As we double our concentration, the rate doubles. Its a direct relationship.

31 Chemical Kinetics Sketch a graph with concentration on Y and time on X axis- Label axis!! Integrated Rate laws We look for straight lines. This provides a clean visual about the relationship of concentration and time. This does not provide a straight line

32 Chemical Kinetics Sketch a graph with concentration on Y and time on X axis- Label axis!! Integrated Rate laws We can manipulate the data to provide a straight line plot. Change how we plot concentration. Natural log x Concentration In [A] Slope is negative (-k)

33 Chemical Kinetics The Change of Concentration with Time Take equations and and smash them together. Rate = - [A] t = k[A]

34 Chemical Kinetics The Change of Concentration with Time How do you use this equation to solve for concentration? Using calculus to integrate the rate law for a first-order process gives us ln [A] t [A] 0 = kt Where [A] 0 is the initial concentration of A. [A] t is the concentration of A at some time, t, during the course of the reaction.

35 Chemical Kinetics Integrated Rate Laws Manipulating this equation produces… ln [A] t [A] 0 = kt ln [A] t ln [A] 0 = kt ln [A] t = kt + ln [A] 0 …which is in the form y = mx + b

36 Chemical Kinetics First-Order Processes Therefore, if a reaction is first-order, a plot of ln [A] vs. t will yield a straight line, and the slope of the line will be -k. ln [A] t = -kt + ln [A] 0 Relate this equation to the slope.

37 Chemical Kinetics The decomposition of a certain insecticide in water at 12 C follows first-order kinetics with a rate constant of 1.45 yr 1. A quantity of this insecticide is washed into a lake on June 1, leading to a concentration of g/cm 3. Assume that the average temperature of the lake is 12 ºC. (a) What is the concentration of the insecticide on June 1 of the following year? (b) How long will it take for the insecticide concentration to decrease to –7 g/cm 3 ? PLUG & CHUG Sample Exercise 14.5 Using the Integrated First-Order Rate Law ln[insecticide] t -1 yr = ( 14.51) k = 1.45 yr -1 ln [A] 0 = [5.0 x g/cm 3 ] t = 1 year ln [insecticide] t-1yr = [X] -(1.45 yr -1 ) SET IT UP (1 year) ln [insectacide] t-1yr = + ln [5.0 x g/cm 3 ] Get rid of ln by e x on both sides ln[insecticide] t - 1 yr = [insecticide] t = 1 yr = e = g/cm 3

38 Chemical Kinetics The decomposition of a certain insecticide in water at 12 C follows first-order kinetics with a rate constant of 1.45 yr 1. A quantity of this insecticide is washed into a lake on June 1, leading to a concentration of g/cm 3. Assume that the average temperature of the lake is 12 ºC. (a) What is the concentration of the insecticide on June 1 of the following year? (b) How long will it take for the insecticide concentration to decrease to –7 g/cm 3 ? PLUG & CHUG Sample Exercise 14.5 Using the Integrated First-Order Rate Law k = 1.45 yr -1 ln [A] 0 = [5.0 x g/cm 3 ] t = X ln [ ] t = -(1.45 yr -1 ) SET IT UP X ln [ ] t = + ln [5.0 x g/cm 3 ] Get X by itself- move to left side 1.45 yr -1 =X ln [ ] t - ln [5.0 x g/cm 3 ] 1.45 yr =0.35 years

39 Chemical Kinetics Practice Exercise The decomposition of dimethyl ether, (CH 3 ) 2 O, at 510 ºC is a first-order process with a rate constant of –4 s –1 : (CH 3 ) 2 O(g) CH 4 (g) + H 2 (g) + CO(g) If the initial pressure of (CH 3 ) 2 O is 135 torr, what is its pressure after 1420 s? Continued Sample Exercise 14.5 Using the Integrated First-Order Rate Law ln[torr] t = (4.91) k = 6.8 x s -1 ln [A] 0 = [135 torr] t = 1420 s ln [X torr] t = [X] -(6.8 x ) SET IT UP (1420 s)ln [X torr] t = + ln [135 torr] Get rid of ln by e x on both sides ln[torr] t = 3.94 [torr] t = e 3.94 = 51.6 torr

40 Chemical Kinetics The Change of Concentration with Time Describe a second-order reaction. When you double the reactant the rate increases by a power of 2, to quadruple the rate

41 Chemical Kinetics Sketch a graph with rate on Y and concentration on X axis- Label axis!! The relationship is more pronounced. Double your concentration and the rate goes up by the power of 2. Hence- second order.

42 Chemical Kinetics Sketch a graph with concentration on Y and time on X axis- Label axis!! Integrated Rate laws We look for straight lines. This provides a clean visual about the relationship of concentration and time. This does not provide a straight line

43 Chemical Kinetics Sketch a graph with concentration on Y and time on X axis- Label axis!! Integrated Rate laws We can manipulate the data to provide a straight line plot. Change how we plot concentration. 1 divided by Concentration 1/[A] And the slope is positive (k)

44 Chemical Kinetics Second-Order Processes Similarly, integrating the rate law for a process that is second-order in reactant A, we get 1 [A] t = kt + 1 [A] 0 also in the form y = mx + b Provide the second order equation.

45 Chemical Kinetics Second-Order Processes So if a process is second-order in A, a plot of 1/[A] vs. t will yield a straight line, and the slope of that line is k. 1 [A] t = kt + 1 [A] 0

46 Chemical Kinetics The Change of Concentration with Time What does second order reactions depend on? A second order reaction is one whose rate depends on the initial reactant concentration

47 Chemical Kinetics Second-Order Processes The decomposition of NO 2 at 300°C is described by the equation NO 2 (g) NO (g) + 1/2 O 2 (g) and yields data comparable to this: Time (s)[NO 2 ], M

48 Chemical Kinetics Second-Order Processes Graphing ln [NO 2 ] vs. t yields: Time (s)[NO 2 ], Mln [NO 2 ] The plot is not a straight line, so the process is not first-order in [A].

49 Chemical Kinetics Second-Order Processes Graphing ln 1/[NO 2 ] vs. t, however, gives this plot. Time (s)[NO 2 ], M1/[NO 2 ] Because this is a straight line, the process is second- order in [A].

50 Chemical Kinetics

51 Chemical Kinetics Practice with graphs- After creating regression graphs of various reactions, provide the rate order for each graph. What order is this reaction and what formula would I use to calculate various times/concentrations? First order and

52 Chemical Kinetics Practice with graphs- After creating regression graphs of various reactions, provide the rate order for each graph. What order is this reaction and what formula would I use to calculate various times/concentrations? Zero order and

53 Chemical Kinetics Practice with graphs- After creating regression graphs of various reactions, provide the rate order for each graph. What order is this reaction and what formula would I use to calculate various times/concentrations? Second order and

54 Chemical Kinetics


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