exam_3_132_2006_solutions

exam_3_132_2006_solutions - Chemistry 132 Hour Examination...

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Chemistry 132 Hour Examination 3 April 20, 2006 Name ( PRINT)______ SOLUTIONS __________ Student number____________________________ Workshop Leader__________________________ 1. (30 points ) ____________________ 2. (35 points ) ____________________ 3. (25 points ) ____________________ 4. (40 points ) ____________________ TOTAL (130 points ) Show your work neatly and circle your answers . Give correct units for answers requiring them. The last two pages of the exam consist of a sheet of potentially useful formulas and a Periodic Table. You may detach these sheets.
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2 1. (30 points) The Zeldovic mechanism is a very important pathway in combustion processes in which NO is produced by oxidation of the nitrogen occurring in air. The first step in this mechanism is the following reaction: O + N 2 NO + N The activation energy for this reaction is 319.0 kJ/mol, and the reaction is endothermic by 313.8 kJ/mol. a) Make a sketch of the reaction coordinate for this reaction. b) At 1500K, the rate constant for the reaction is 8.4 × 10 9 M -1 s -1 . Calculate the temperature for which the rate constant is 1 × 10 12 M -1 s -1 ln(k 2 /k 1 ) = -E a /R(1/T 2 – 1/T 1 ) ln( 1 × 10 12 / 8.4 × 10 9 ) = -(319,000/8.31)(1/T 2 – 1/1500) ln (119.5) = -(3.84 × 10 4 )(1/T 2 – 1/1500) -4.783/(3.84 × 10 4 ) + 1/1500 = 1/T 2 -1.257 × 10 -4 + 6.667 × 10 -4 = 5.410 × 10 -4 T 2 = 1850 K O + N 2 NO + N E a = 319 kJ 313.8 kJ
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3 2. (35 points) Radium-226 ( Ra 226 88 ) decays with a half-life of 1622 years. (One year = 3.15 × 10 7 s ). Its principal decay pathway is by emission of α -particles. An α -particle is a He 4 2 nucleus. a) Write a balanced nuclear reaction for this decay process. b) Using the following masses, calculate the energy liberated in MeV for this decay process. Masses:
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This note was uploaded on 04/16/2008 for the course CHM 132 taught by Professor Farrar during the Spring '08 term at Rochester.

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exam_3_132_2006_solutions - Chemistry 132 Hour Examination...

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