AP Chapter 13: Kinetics Name

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1 AP Chapter 13: Kinetics Name Warm-Ups (Show your work for credit) Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8.

2 AP Chapter 13: Kinetics 2 Warm-Ups (Show your work for credit) Date 1. Date 2. Date 3. Date 4. Date 5. Date 6. Date 7. Date 8.

3 AP Chapter 13: Kinetics 3 Warm-ups and problems will be collected before you take the test. Read Chapter 13: Chemical Kinetics Answer the following problems in the space provided. For problems involving an equation, carry out the following steps: 1. Write the equation. 2. Substitute numbers and units. 3. Show the final answer with units. There is no credit without showing work. Activation Energy and Collision Theory 1. The burning of methane in oxygen is a highly exothermic reaction. Yet a mixture of methane and oxygen gas can be kept indefinitely at room temperature without any apparent change. Explain. 2. Sketch a potential energy versus reaction progress plot for the following reactions: (a) S(s) + O 2(g) SO 2(g) H = kj (b) Cl 2(g) Cl(g) + Cl(g) H = kj 3. Explain, in terms of the Boltzmann energy distribution, why increasing temperature increases reaction rate. 4. Write the Arrhenius equation and define each term. What does the frequency factor measure? 5. When 6 g of granulated Zn is added to a solution of 2M HC1 in a beaker at room temperature, hydrogen gas is generated. Write the balanced equation for this reaction. For the following changes (at constant volume of the acid), state whether the rate of hydrogen gas evolution will be increased, decreased, or unchanged. Explain each in terms of collision theory. a. 6 g of powdered Zn is used. b. 4 g of granulated Zn is used.

4 AP Chapter 13: Kinetics 4 c. 2M acetic acid is used instead of 2M HC1. d. Temperature is raised to 40 C. The Rate of a Reaction 6. For the reaction: A B, (a) Write the rate of reaction in terms of A. (b) Write the rate of reaction in terms of B. 7. Write the reaction rate expressions for the following reactions in terms of the disappearance of the reactants and the appearance of products: (a) 2H 2(g) + O 2(g) 2H 2O(g) (b) 4NH 3(g) + 5O 2(g) 4NO(g) + 6H 2O(g) 8. Consider the reaction: 3H 2 + N 2(g) 2NH 3(g) Suppose that at a particular moment during the reaction molecular hydrogen is reacting at the rate of M/s. (a) At what rate is ammonia being formed? (b) At what rate is molecular nitrogen reacting? 9. For this reaction: 2H2(g) + 2NO(g) 2H2O(g) + N2(g), (a) Write the rate law, using generalized exponents a and b. (b) What is the order of the reaction with respect to each reactant and what is the overall order of the reaction? (c) Which symbol in the rate law is temperature dependent?

5 AP Chapter 13: Kinetics 5 The Rate Law 10. Consider the reaction: X + Y Z. From the following data, obtained at 360K: INITIAL RATE OF DISAPPEARANCE OF X (M/s) [X] [Y] (a) Determine the order of the reaction with respect to each reactant. (b) Determine the rate constant (including units). (c) Write the rate law. (d) Determine the initial rate of disappearance of X when the [X] is 0.30 M and [Y] is 0.40 M. 11. The following data were collected for the reaction between hydrogen and nitric oxide at 700 C: (a) Determine the order of the reaction. 2H 2(g) + 2NO(g) 2H 2O(g) + N 2(g) EXPERIMENT [H 2] [NO] INITIAL RATE (M/s) E E E-6 (b) Calculate the rate constant. (c) Write the rate law.

6 AP Chapter 13: Kinetics The bromination of acetone is an example of an acid-catalyzed reaction: CH 3COCH 3 + Br 2 CH 3COCH 2Br + H + + Br - The rate of disappearance of bromine was measured for several different concentrations of acetone, bromine, and H + ions at a certain temperature: RUN # [CH 3COCH 3] [Br 2] [H + ] Rate of Disappearance of Br2 (M/s) E E E E E-5 (a) Determine the order of the reaction. H + (b) Calculate the rate constant. (c) Write the rate law. (d) What is the rate of the reaction for [CH 3COCH 3] = 0.35M, [Br 2] = 0.15M, and [H + ] = 0.20M? Integrated Rate Law: The Relationship between Reactant Concentration and Time 13. The thermal decomposition of phosphine (PH 3) into phosphorus and molecular hydrogen is a first-order reaction with a half-life of 35.0 s at 680 C: 4PH 3(g) P 4(g) + 6H 2(g) a. Calculate the first-order rate constant for the reaction. b. Write the rate law. c. Calculate the time required for 95 percent of the phosphine to decompose.

7 AP Chapter 13: Kinetics The rate constant for the following second-order reaction is 0.80/M s at 10 C: 2NOBr(g) 2NO(g) + Br 2(g) a. Starting with a concentration of M, calculate the concentration of NOBr after 22 s. b. Calculate the half-lives when [NOBr] 0 = M and [NOBr] 0 = M. 15. The rate constant for the second-order reaction: 2NO 2(g) 2NO(g) + O 2(g) is 0.54/M s at 300 C. How long (in seconds) would it take for the concentration of NO 2 to decrease from 0.62 M to 0.28 M? 16. The rate of the reaction: CH 3COOC 2H 5(aq) + H 2O(l) CH 3COOH(aq) + C 2H 5OH(aq) shows first-order characteristics (that is, rate = k[ch 3COOC 2H 5]) even though this is a second-order reaction (first order in CH 3COOC 2H 5 and first order in H 2O). Explain. 17. The decomposition of N 2O to N 2 and O 2 is a first-order reaction. At 730 C the half-life of the reaction is 3.58 x 10 3 min. If the initial pressure of N 2O is 2.10 atm at 730 C, calculate the total gas pressure after one half-life. Assume that the volume remains constant. 18. A certain first-order reaction is 35.5 percent complete in 4.90 min at 25 C. What is its rate constant?

8 AP Chapter 13: Kinetics The rate of the reaction: NO 2(g) + CO(g) NO(g) + CO 2(g) depends only on the concentration of nitrogen dioxide below 225 o C. At 200 o C, the following data were collected: (a) Determine the order of the reaction. TIME (s) [NO 2] E E E E E (b) Write the integrated rate law. (c) Determine the rate constant. (d) Write the rate law. 20. The following gas-phase reaction was studied at 290 C by observing the pressure as a function of time in a constant-volume vessel: ClCO 2CCl 3(g) 2COCl 2(g) (a) Determine the order of the reaction. TIME (s) P of ClCO 2CCl 3 (mm Hg) (b) Write the integrated rate law. (c) Determine the rate constant. (d) Write the rate law.

9 AP Chapter 13: Kinetics Radioactive plutonium-239 (t 1/2 = 2.44 x 10 5 yr) is used in nuclear reactors and atomic bombs. If there is 5.0 x 10 2 g of the isotope in a small atomic bomb, how long will it take for the substance to decay to 1.0 x 10 2 g, too small an amount for an effective bomb? 22. Fill in the chart summarizing rate law equations for the chemical reaction: A products. Know what is on the reference tables and memorize the rest! Rate Law Equation Integrated Rate Law Equation Variables for Straight Line Plot Relationship of k and Slope k units Half-Life Equation Zeroth Order First Order Second Order Reaction Mechanisms 23. The equation for the combustion of ethane (C 2H 6) is 2C 2H 6(g) + 7O 2(g) 4CO 2(g) + 6H 2O(l) Explain why it is unlikely that this equation also represents the elementary step for the reaction. 24. For the reaction X 2 + Y + Z XY + XZ it is found that doubling the concentration of X 2 doubles the reaction rate, tripling the concentration of Y triples the rate, and doubling the concentration of Z has no effect, (a) What is the rate law for this reaction? (b) Why is it that the change in the concentration of Z has no effect on the rate? (c) Suggest a mechanism for the reaction that is consistent with the rate law.

10 AP Chapter 13: Kinetics The mechanism for the reaction of nitrogen dioxide with carbon monoxide to form nitric acid (nitrogen dioxide gas) and carbon dioxide is thought to be: NO 2 + NO 2 NO 3 + NO (slow) NO 3 + CO NO 2 + CO 2 (fast) a. Write the rate law based on this mechanism. b. Write the overall balanced equation. c. Which chemical species would be needed to be identified to help verify this mechanism? 26. The rate law for the decomposition of ozone to molecular oxygen, 2O 3(g) 3O 2(g) is rate = k[o 3] 2 / [O 2]. The mechanism proposed for this process is O 3 O + O 2 (fast) O + O 3 2O 2 (slow) a. Derive the rate law from these elementary steps. b. Explain why the rate decreases with increasing O 2 concentration. 27. The rate law for the reaction: 2H 2(g) + 2NO(g) N 2(g) + 2H 2O(g) is rate = k[h 2][NO] 2. Which of the following mechanisms are possible for this reaction? Mechanism I H 2 + NO H 2O + N (slow) N + NO N 2 + O (fast) O + H 2 H 2O (fast) Mechanism II H 2 + 2NO N 2O + H 2O (slow) N 2O + H 2 N 2 + H 2O (fast) Mechanism III 2NO N 2O 2 (fast equilibrium) N 2O 2 + H 2 N 2O + H 2O (slow) N 2O + H 2 N 2 + H 2O (fast)

11 AP Chapter 13: Kinetics It is usually difficult to propose a mechanism that is both consistent with the rate law and the overall balanced equation. For the reaction in problem 11, propose a mechanism. Catalysts 29. Consider the following mechanism for the enzyme-catalyzed reaction: E + S ES (fast equilibrium) ES E + P (slow) Derive an expression for the rate law of the reaction in terms of the concentrations of E and S. 30. When looking at a reaction mechanism, how can you tell the difference between a catalyst and an intermediate? 31. What is the difference between homogeneous and heterogeneous catalysis? 32. Many reactions are said to be acid catalyzed. What chemical species is the catalyst in these reactions? 33. Is it probable that a catalyzed and uncatalyzed reaction have the same rate law? Explain. Review 34. A volume of a sample of pure HCl gas was 235 ml at 27 o C and 87.4 mmhg. It was completely dissolved in water and titrated with Ba(OH) 2 solution. A volume of 11.4 ml of the Ba(OH) 2 solution were required to neutralize the HCl. What is the molarity of the Ba(OH) 2 solution?