Kinetics Practice Test 2017 Name: date: 1. Use the data provided the answer the question.

Transcription

1 Kinetics Practice Test 2017 Name: date: 1. Use the data provided the answer the question. The data above was obtained for a reaction in which X + Y Z. Which of the following is the rate law for the reaction? a. Rate = k[x] 2 b. Rate = k[y] 2 c. Rate = k[x][y] d. Rate = k[x] 2 [Y] e. Rate = k[x][y] 2 2. If the oxygen isotope 20 O has a half-life of 15 seconds, what fraction of the sample of pure 20 O remains after 1.0 minutes? a. ½ b. ¼ c. 7/30 d. 1/8 e. 1/16 3. Pure substance X decomposes from X products. Which of the following graphs indicates that the rate of the decomposition is second order in X? 4. The role of a catalyst in ca chemical reaction is to: a. Decrease the amount of reactants that must be used b. Lower the activation energy for the reaction c. Supply the activation energy required for the reaction to proceed

2 d. Increase the amounts of products formed at equilibrium e. Increase the entropy change for the reaction 5. Which of the following statements is a correct interpretation of the data below regarding how the order of the reaction can be determined? a. The reaction must be first order because there is only one reactant species. b. The reaction is first order if the plot of the ln [H2O2] vs. time is a straight line. c. The reaction is first order if the plot of 1/[H2O2] is a straight line. d. The reaction is second order because 2 is the coefficient of H2O2 in the chemical equation. 6. When free Cl (g) atoms encounter O3 (g) molecules in the upper atmosphere, the following reaction mechanism is proposed to occur. Which of the following rate laws for the overall reaction corresponds to the proposed mechanism? 7. Which of the following reaction energy profiles best corresponds to the proposed mechanism in the previous problem?

3 8. In order to determine the order of the reaction represented below, the initial rate of formation of XY 2 is measured using different initial values of [X] and [Y]. X(g) + 2 Y (g) XY 2 (g) The results of the experiment are show in the table below. In trial 2 which of the reactants would be consumed more rapidly, and why? a. X, because it has a higher molar concentration. b. X, because the reaction is second order with respect to X. c. Y, because the reaction is second order with respect to Y. d. Y, because the rate of disappearance will be double that of X. 9. Which of the following will most likely increase the rate of the following reaction: C 2 H 4 (g) + H 2 (g) C 2 H 6 (g) a. Decreasing the temperature of the reaction system b. Adding a heterogeneous catalyst to the reaction system c. Increasing the volume of the reaction vessel using a piston d. Removing some H 2 (g) from the reaction system. 10. The rate law for the reaction below is represented as rate = k [NO2][F2]. Which of the following could be the first elementary step of a two-step mechanism for the reaction if the first step is slow and the second step is fast?

4 2 NO 2 (g) + F 2 (g) 2 NO 2 F (g) 11. Approximately how long did it take for 75% of the initial amount of C25H30N3 + (aq) to react? a. 75 s b. 225 s c. 300 s d. 600 s 12. In the question above, what would be the effect on the reaction rate if the solution of C25H30N3 + (aq) is diluted by a factor of 2? a. It would be higher b. It would be lower c. It would not change d. It would initially be higher, but then rapidly decrease. 13. Use the same reaction and data presented in problem #11. Observe the following data to answer the question below:

5 The student wants to use the spectrophotometer to measure [C25H30N3 + ] with the greatest sensitivity as the reaction progresses. Which of the following indicates the best wavelength setting and explains why it is the best? a. 205 nm because the colorless form of the molecule will absorb significantly at this wavelength b. 205 nm because both forms of the molecule will absorb significantly at this wavelength c. 590 nm because only the violet form of the molecule will absorb significantly at this wavelength d. 590 nm because this wavelength falls in the violet region of the visible light spectrum. Written Section: 1. NO (g) reacts with Br2 (g), as represented by the equation below. 2NO (g) + Br2 (g) 2 NOBr (g) An experiment was performed to study the rate of the reaction at 546 K. Data from these trials are show below. Trial Initial [NO] (M) Initial [Br2] (M) Initial Rate of Consumption of Br2 (M/s) a. Using the data in the table, determine the order of the reaction with respect to each of the following reactants. Justify your answer: i. Br2 ii. NO b. Write the rate law for the reaction. c. Determine the value of the rate law constant, k, for the reaction. Include units with your answer. d. At a later time during trial 2, the concentration of Br2 (g) is determined to be 0.16M. i. Determine the concentration of NO (g) at that time. ii. Calculate the rate of consumption of Br2 (g) at that time. A proposed 2 step mechanism for the reaction is represented below. Step 1: NO + Br2 NOBr2 slow (rate determining step) Step 2: NO + NOBr2 2 NOBr fast e. Is the proposed mechanism consistent with the rate law determined in part b? Justify your answer.