1 CHEM 123N FOUNDATIONS OF CHEMISTRY/PRINCIPLES OF CHEMISTRY Unit Exam 2, Wednesday, October 9th, 2013 Dr. Patricia Pleban, 4:20 – 5:35 pm TR section, CRN 14768 Print (Last, First Name)_______KEY______________ UIN ______________________ By taking this exam, you are acknowledging that you will follow the ODU HONOR CODE. Please write your name on each page of the exam. Recitation Instructor (please check your recitation time under your instructor’s name): Lenora Harper _____ 3:00 – 3:50 pm, Friday _____4:20 – 5:10 pm, Friday Patricia Lutz _____8:30 – 9:20 am, Thursday _____9:30 – 10:20 am, Thursday _____10:30 – 11:30 am, Thursday _____11:30 am – 12:20 pm, Thursday See Page 2 for Instructions & Notes2 PLEASE NOTE:  By taking this exam and signing your name above, you are acknowledging that you will follow the ODU HONOR CODE.  On the first page, fill in your student information. Additionally, you should write your name at the top of every page on this test.  Multiple choice answers should be bubbled in on your blue scantron (200-question, 5-answer format) using your No. 2 pencil. Your answer on your scantron is your final answer – there is a space next to the multiple choice question number where you may write your answer as a record (for you only).  All answers to the short answer questions must be in the space provided with the question. Work and answers on scratch paper will not be graded. Please circle your answer.  Exam time: 80 minutes for both the multiple choice and short answer sections  Note: This is a closed book exam. Only the formula/constant/instruction sheets included as part of this test packet and a non-programmable calculator are allowed. No other books, notes or electronic devices are authorized. Use of these items will be interpreted as an Honor Code violation.  A periodic table is given on page 11 and any additional given information can be found at on page 10. Use pages 10 & 12 for scratch paper.  Points: Each multiple choice question (pages 3-6) is worth 5 points for a total of 90 points. The short answer (pages 7-9) is worth 30 points. Total test points = 121 points graded out of 100.3 CHEM 123N Foundations of Chemistry II Fall Semester 2013, Exam 1, October 9th Print (Last, First Name)__________KEY__________________________________ UIN ______________________ By taking this exam, you are acknowledging that you will follow the ODU HONOR CODE. Please write your name on each page of the exam. Exam time: 80 minutes Note: This is a closed book exam. Only the formula/constant/instruction sheets included as part of this test packet and a non-programmable calculator are allowed. No other books, notes or electronic devices are authorized. Use of these items will be interpreted as an Honor Code violation. Bubble in your name and UIN on the OPSCAN sheet! Please write the letter of the best answer in the space next to the question and then code this letter in the row beside the question number on the OPSCAN sheet provided. The answer on the OPSCAN sheet is your final answer. Write the answers to the Free Response questions 19 -21 (pg 7-9) on this exam. Please allow ±2 in last significant digit for rounding error. Given information is on p. 10 & 11 (Periodic Table). 1._D____ The decomposition of dinitrogen pentoxide is described by the chemical equation 2 N2O5(g) → 4 NO2(g) + O2(g) If the rate of appearance of O2 is equal to 0.560 mol/min at a particular moment, what is the rate of appearance of NO2 at that moment? A) 0.140 mol/min B) 0.280 mol/min C) 1.12 mol/min D) 2.24 mol/min E) None of these 2.__C___ For a reaction that follows the general rate law, Rate = k[A][B]2, what will happen to the rate of reaction if the concentration of A is increased by a factor of 3.00? The rate will A) decrease by a factor of 1/9.00. B) decrease by a factor of 1/3.00. C) increase by a factor of 3.00. D) increase by a factor of 9.00. E) increase by a factor of 2 3.__B__ The first-order reaction, 2 N2O(g) → 2 N2(g) + O2(g), has a rate constant equal to 0.76 s-1 at 1000 K. How long will it take for the concentration of N2O to decrease to 42% of its initial concentration at 1000 K? ln (0.42) = - 0.76 s-1t Take inverse ln of both sides and solve for t [A]/[A]0 = fraction remaining A) 0.88 s B) 1.1 s C) 1.8 s D) 2.4 s E) 2.8 s 4._D___ The rate constant, k, for a first-order reaction is equal to 4.2 × 10-4 s-1. What is the half-life for the reaction? A) 2.9 × 10-4 s B) 1.0 × 103 s C) 1.4 × 103 s D) 1.7 × 103 s E) 2.4 × 103 s4 5.__E___ In aqueous solution, hypobromite ion, BrO-, reacts to produce bromate ion, BrO3-, and bromide ion, Br-, according to the following chemical equation. 3 BrO-(aq) → BrO3-(aq) + 2Br-(aq) A plot of 1/[BrO-] vs. time is linear and the slope is equal to 0.056 M-1s-1. If the initial concentration of BrO- is 0.80 M, how long will it take one-half of the BrO- ion to react? 2nd order reaction. ½ of 0.80 is 0.40 M (1/0.40 M) = 0.056 M-1s-1 t + (1/0.80 M) A) 4.5 × 10-2 s B) 7.1 s C) 12 s D) 18 s E) 22 s 6.__A___ For the zeroth-order reaction: C → products, -Δ[C]/Δt = k, which of the following graphs would be expected to give a straight line? A) [C] vs. t B) ln[C] vs. t C) 1/[C] vs. t D) [C]2 vs. t E) None will be linear 7.__A___ What is the minimum energy barrier that must be overcome for a chemical reaction to occur? A) activation energy B) reaction enthalpy C) potential entropy D) vaporization enthalpy 8._B___ The addition of water to Fe(phen)32+ in acid solution takes place according to the equation: Fe(phen)32+ + 3 H3O+ + 3 H2O → Fe(H2O)62+ + 3 phenH+. If the activation energy, Ea, is 126 kJ/mol and the rate constant at 30°C is 9.8 × 10-3 min-1, what is the rate constant at 50°C? ln (k2/9.8 x 10-3min-1) = [- 126000 J/(8.314 J/mol K)][(1/323 K) – (1/303 K)] A) 4.4 × 10-4 min-1 B) 2.2 × 10-1 min-1 C) 4.6 × 10-1 min-1 D) 2.3 × 103 min-1 E) None of these 9.__A___ A mechanism for a naturally-occurring reaction that destroys ozone is: Step 1: O3(g) + HO(g) →