U N I T T E S T P R A C T I C E

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1 South Pasadena AP Chemistry Name 2 Chemical Kinetics Period Date U N I T T E S T P R A C T I C E Part 1 Multiple Choice You should allocate 30 minutes to finish this portion of the test. No calculator should be used. A periodic table and data table will be provided. Select the answer that best responds to each question. 1. Consider the following concentration vs. time graph: Which of the following reasons provide the strongest evidence that the equation for the reaction is: 3A + B C + 3D? (A) B ran out faster than A. (B) Neither the graph for A nor B is linear. (C) The initial concentration of A is three times greater than the initial concentration of B. (D) The initial slope of A is three times greater than the initial slope of B. 2. In the reaction 3 O 2 (g) 2 O 3 (g), the rate of disappearance of O 2 is 0.60 M/s. What is the rate of appearance of O 3? (A) 0.40 M/s (B) 0.60 M/s (C) 0.90 M/s (D) 1.20 M/s 3. Consider the reaction: X + 2Y Z rate = k[x] 1 [Y] 1 In an experiment in which [X] = [Y] = 0.10 M, the initial rate was found to be R M/s. With which of the following initial concentrations will the rate double to 2R M/s? (A) [X] = 0.10 M, [Y] = 0.40 M (B) [X] = 0.20 M, [Y] = 0.20 M (C) [X] = 0.40 M, [Y] = 0.05 M (D) [X] = 0.40 M, [Y] = 0.20 M 4. Consider the following data for the reaction: 2 NO (g) + O 2 (g) 2 NO 2 (g) Trial [NO] [O 2] Rate M 0.10 M 5.0 M/s M 0.10 M 10.0 M/s M 0.20 M 20.0 M/s What is the rate law for this reaction? (A) Rate = k[no] 1 (B) Rate = k[no] 2 (C) Rate = k[no] 1 [O 2] 1 (D) Rate = k[no] 2 [O 2] 1 5. The decomposition of ammonia is a zero order reaction: 2 NH 3 (g) N 2 (g) + 3 H 2 (g) When mol NH 3 is placed in a 1.00 L container, mol N 2 (g) is produced after 40.0 min. What is the value of the rate constant, k? (A) M min 1 (B) M min 1 (C) M min 1 (D) M min 1 6. An experiment was carried out to find the kinetics of the following reaction: 3 C D + E The data was collected and plotted, and it was found that when ln [C] was plotted against time, a linear graph was produced. Which of the following is expected to be true? (A) The graph of [C] vs. time is linear. (B) The half life of the reaction is constant throughout the experiment. (C) The rate determining step for the reaction mechanism could be 2 C E. (D) The rate of reaction is constant throughout the experiment.

2 7. Consider the first order reaction: SO 2Cl 2 (l) SO 2 (g) + Cl 2 (g) The kinetics graph below was prepared: Which of the following could describe this graph? (A) [SO 2Cl 2] vs. time (B) ln [SO 2Cl 2] vs. time (C) ln k vs. 1/time (D) Rate of SO 2Cl 2 vs. [SO 2Cl 2] 8. An experiment for the reaction A B was performed, and the time at various concentrations of A was recorded. [A] M M M M time 0 s 10.1 s 19.8 s 30.2 s Which of the following is likely the rate law for the reaction? (A) Rate = k[a] 0 (B) Rate = kla] 1 (C) Rate = k[a] 2 (D) Rate = k[a] 3 9. A 3% H 2O 2 solution is placed in beaker A, and a 30% H 2O 2 solution is placed in beaker B, both at the same temperature. When equal amounts of a KI solution is added to each beaker, the reaction is beaker B proceeds noticeably faster than that in beaker A. Which of the following accounts for the observation? (A) The concentration of H 2O 2 in beaker is greater, so beaker B has more effective collisions than beaker A. (B) There is more KI in beaker B to catalyze the reaction. (C) The KI in beaker A is an inhibitor, slowing down the reaction. (D) The molecules in beaker B are moving faster than those in beaker A, so the reaction proceeds faster. 10. The following reaction is sped up by in the presence of platinum, Pt (s): C 2H 4 (g) + H 2 (g) C 2H 6 (g) Which of the following is true about this reaction? (A) Pt is an acid-base catalyst, allowing the rapid transfer of hydrogen. (B) Pt is in excess, but will eventually get used up. (C) The presence of Pt provides an reaction pathway with an activation energy lower than that without Pt. (D) The presence of Pt lowers value of the rate constant, k. 11. The potential energy graph for various conformations of butane, C 4H 10, is shown. (The x- axis represents the torsional angle, or the angle between the near and far methyl ( CH 3) groups.) At which torsional angle is the compound most stable? (A) 0 (B) 60 (C) 120 (D) 180

3 12. The Maxwell-Boltzmann distributions for two samples of a reaction mixture, T1 and T2, are shown below. 14. Consider the following reaction mechanism: Step 1: A + B C Step 2: C + B D The following potential energy graph was obtained: Which of the following true? (A) The reaction proceeds faster in T2 because more molecules are colliding with sufficient kinetic energy. (B) The reaction proceeds faster in T2 because a catalyst is added resulting in more molecules to overcome the activation energy. (C) The reaction proceeds faster in T1 because there are more molecules in that sample. (D) The reaction proceeds faster in T1 because it has a higher average kinetic energy. 13. Consider the following Arrhenius Equation graphs for two experiments ln k I Potential energy Reaction Progress Which of the following is true? (A) The reaction is endothermic. (B) Step 1 is the slow step in the mechanism. (C) Substance C is the transition state. (D) The rate law is rate = k[a] 1 [B] Assume a reaction occurs by the mechanism given below. What is the rate law for the reaction? Step 1: A + B C fast equilibrium Step 2: 2 C D slow (A) rate = k[a] 2 (B) rate = k[a] 1 [B] 1 (C) rate = k[a] 2 [B] 2 (D) rate = k[a] 1 [B] 1 [C] 1 II 1/T Which of the following is true: (A) The reaction in Experiment I was faster because a catalyst was added. (B) The reaction in Experiment I was faster because it took place at a higher temperature. (C) The reaction in Experiment II was faster because it there was a greater concentration of reactants. (D) The reaction in Experiment II was faster because a catalyst was added.

4 Part 2 Free Response You should allocate 30 minutes to finish this portion of the test. You may use a scientific calculator. A periodic table and data table will be provided. Respond to each part of the questions completely. Be sure to show your work clearly for questions that involve calculators. 16. Consider the following reaction: 2 SO 2 (g) + O 2 (g) 2 SO 3 (g) H rxn = 198 kj/mol The following data for kinetics experiments were taken at 25 C: Experiment [SO 2] (mol L 1 ) [O 2] (mol L 1 ) Initial Rate of Disappearance of SO 2 (mol L 1 s 1 ) ? (a) Find the order with respect to each reactant. Write the rate law expression Trials 1 & 3: = k(0.30)x (0.10) y k(0.10) x (0.10) y 9 = 3 x x = 2 Reaction is 2 nd order with respect to SO 2. Trials 1 & 2: = k(0.20)2 (0.20) y k(0.10) 2 (0.10) y 4 = 4 2 y y = 0 Reaction is 0 th order with respect to O 2. Rate = k[so 2] 2 [O 2] 0 (b) Determine the value for the rate constant. Include the units. k = rate [SO 2] 2 = M/s (0.10 M) 2 = M 1 s 1 (c) Calculate the initial rate of disappearance of SO 2 in experiment 4. Rate = k[so 2] 2 = ( M 1 s 1 )(0.50 M) 2 = M/s (d) Calculate the rate of appearance of SO 3 for experiment 2. [SO 3] = [SO2] = t t 4 M/s (e) For experiment 1, calculate the [SO 2] after 100. seconds had elapsed. 1 1 = +k t [SO 2] 100 [SO 2] = +( M/s)(100 s) [SO 2] M [SO 2] 100 = M

5 (f) The following mechanisms were proposed for this reaction. Mechanism I Step 1: SO 2 + O 2 SO 3 + O (fast equilibrium) Step 2: SO 2 + O SO 3 (slow) Mechanism II Step 1: 2 SO 2 S 2O 4 Step 2: 2S 2O 4 + O 2 2 SO 3 Mechanism III Step 1: O 2 2 O Step 2: SO 2 + O SO 3 Step 3: SO 2 + O SO 3 (slow) (fast) (slow) (fast) (fast) (i) Determine which one is consistent with the given data. Justify your answer. Mechanism II is consistent with the data. The rate determining step is step 1, so the rate law for Mechanism II is rate = k[so 2] 2 (Rate law for Mechanism I is rate = k[so2] 2 [O 2]/[SO 3]. Rate Law for Mechanism III is rate = k[o 2]) (ii) For the selected mechanism, identify the intermediates. Mechanism II: Intermediate: S 2O 4 (g) Sketch the potential energy graph for your selected mechanism in the axes below. Potential Energy Reaction Progress

6 South Pasadena AP Chemistry Name 2 Chemical Kinetics Period Date U N I T T E S T B L U E P R I N T Part 1: Multiple Choice Format: 15 questions, four answer choices: (A)-(D) Expected time: 30 minutes Allowed resources: Periodic Table, Equations and Constants. No calculators. Q# Lesson Topic Objective Concentration vs. Time Graphs Describe the rate of reactant with respect to each chemical in a reaction, including analyzing its [X] vs. time graph Comparing Rates of Substances in a Reaction Describe the rate of reactant with respect to each chemical in a reaction, including analyzing its [X] vs. time graph Rate Laws Write the rate law and finding the value of the rate constant using initial rates data to describe how concentration of reactants affect a reaction s rate Rate Laws Write the rate law and finding the value of the rate constant using initial rates data to describe how concentration of reactants affect a reaction s rate Integrated Rate Laws calculation Calculate the concentration of reactant after a particular time given the reactant s order Integrated Rate Laws Graphs Determine the order (0 th, 1 st, and 2 nd orders only) of a reactant by analyzing the [X] vs. time, ln[x] vs time, and 1/[X] vs. time graphs. 7 Integrated Rate Laws Graphs Determine the order (0 th, 1 st, and 2 nd orders only) of a reactant by analyzing the [X] vs. time, ln[x] vs time, and 1/[X] vs. time graphs Half Lives Explain how the concentration of a reactant affects (or does not affect for 1 st order reactions) its half life. Calculate the reaction s half life Collision Theory List factors that affect how fast a reaction occurs using collision theory Catalysts Explain how a catalyst works to speed up a reaction Potential Energy Graph Explain how changing the temperature or adding a catalyst/inhibitor affects the rate of reaction, using potential energy graph, kinetic energy distribution graph, or the Arrhenius equation Kinetic Energy Distribution Graph Explain how changing the temperature or adding a catalyst/inhibitor affects the rate of reaction, using potential energy graph, kinetic energy distribution graph, or the Arrhenius equation Arrhenius Equation Explain how changing the temperature or adding a catalyst/inhibitor affects the rate of reaction, using potential energy graph, kinetic energy distribution graph, or the Arrhenius equation Mechanisms Analyze the potential energy graph of a reaction mechanism Mechanisms Evaluate whether a proposed mechanism is valid by determining whether it is consistent with the experimentally-determined rate law. Part 2: Free Response Format: o 1 long question (5-8 parts) o 1 short questions (2-4 parts) Expected time: 30 minutes Allowed resources: Periodic Table, Equations and Constants, and scientific calculators. Topics: Any