Exam_1_practice_S2009 - CHIVI 31 Hourly Exam 1 ~—...

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Unformatted text preview: CHIVI 31 Hourly Exam 1. ~— Practice. Closed Book. February 2009 Name: All questions below are multiple choice. Please answer by encirclingyour choice. Q7 is bonus worth extra 15 points. Intermolecular forces: QIA (15 pts.) Ion—dipole interactions are typically greater than dipole—dipole interactions because a. ion—dipole interactions involve the complete transfer of an electron. dipole—dipole interactions involve the complete transfer of charge. ion—dipole interactions involve partial charges. ion—dipole interactions involve water. 9-953" QlB (15 pts.) Based on the phase diagram shown here, which of the following statements is true for this substance? .4. Pressure (aim) 25 Temperature (°C) a. c. It is a liquid at room temperature. Its normal boiling point is at 25°C. b. Its normal melting point is at 25°C. (:1. It is a gas at room temperature. QlC (15 pts.) In which of the following diagrams are the cohesive interactions between molecules in the liquid greater than the adhesive forces between the liquid and the walls of the tube? a a. a c. c b. b d. d Q2A (20 pts.) Which solution would create the higher osmotic pressure (compared to pure water}—one prepared from 1.0 g ofNaCl in 10 mL ofwater or 1.0 g of CsBr in 10 mL ofwater? a. They would have the same osmotic pressures. b. NaCl would give the higher pressure. 0. CsBr would give the higher pressure. (1. It is impossible to tell. QZB (15 pts.) In the process of dialysis, a special semipermeable membrane allows both small molecules and water to pass through, but not large protein molecules. These membranes are used to separate these small molecules and ions from much larger proteins. If a mixture of proteins and small molecules were separated from pure water by a dialysis membrane as shown in the figure, which way would the water and small molecules flow? .:‘ijwéiérioniv"i“i Froteins and small moiecules in water Both water and small molecules would leave the solution and enter the pure water. Only the proteins would pass into the pure water. Water would enter the solution while small molecules would pass into the pure water. Only small molecules would leave the solution; water would not flow. a. b. c. d. QZC (25 pts.) Which of the following ranks the compounds from lowest to highest boiling points? a. C12, NH3, C607 CH3CH20H C. C12H22011, CH4, HF, HZCO b. CZHZ, NaCl, H20, Clng (1. H2, NH3, H20, C12H22011 Thermodynamics: Q3A (15 pts.) At 0 K, the entropy of a perfect crystal is a. > 0. b. = . c. ‘ < 0. d. All three are possible results, depending on the chemical nature of the crystal. QSB (15 pts.) During a spontaneous chemical reaction, it is found that ASsys < O. This means a. AS < 0 c. ASsurlr > 0 (and larger than ASsys). b. ASS“Ir > 0. d. ASsurf < 0 (and smaller than ASS“). Q3C (15 pts.) Of the three modes of molecular motion—Vibration, rotation, and translation—Which requires the greatest amount of energy to cause an excitation from the ground state to the first excited state? a. Vibration b. rotation c. translation (1. They all require the same amount of energy. Q4A (15 pts.) Determine Align for Big) +12(g): 21mg) given Substance S° (J/mol - K) H2(g) 130.58 12(g) 116:73 HI(g) 206.3 a. _4110 J/mol _ K c. 398.75 J/mol - K b. —165.29 J/mol ' K d. 165.29 J/mol - K Q4B (15 pts.) A system is at equilibrium at a given temperature when a. AS 2 0- c. AH = 0. b. AG=0. d. AU=O. Q4C (15 pts.) Hydrogen reacts with nitrogen to form ammonia (NHg) according to the reaction 3 Mg) + N2<g> : 2 NH3(g) The value of AH" is ~92.38 kJ/mol, and that of AS" is —l 98.2 J/rnol - K. Determine AGO at 298 K. a, 5397 x 104 kJ/mol c. —33.32 kJ/mol Q4D (15 pts.) At what temperature (K) is the given reaction at equilibrium? Assume AH° and S° do not change with temperature. 2 N02(g) *— N204(g> —-3 given Substance AH" (kJ/mol) S° (J/mol - K) ' NOz(g) 33.2 240.0 N204(g) 9.2 304.2 a. 0.32 K c. 3.1 K b. 325 K7 (1. 52 K Kinetics: QSA (15 pts.) In the combustion of methane CH4(g) + 2 02(g) e C02(g) + 2 H20 (g) which reactant has the greatest rate of disappearance? a. C114 C. C02 b. 02 d. H20 QSB (25 pts.) Which of the following relations characterizes a reaction of second order with respect to disappearance of species A: [A] = [Ale/(1+[Alok0 1n([A]) = - kt [A] = [No - kt [A] = [Ala eXIX-kt) Q5C (15 pts.) Ammonia gas (NH3) is produced from hydrogen and nitrogen gas according to the following reaction: 3 H2(g) + N2(g) "> 2NH3(g) If the rate of production of ammonia is R(NH3), What is the rate of loss of hydrogen and nitrogen gas, respectively? % R(NHs); é RCNH3) "i R(NH3); 2 R(NH3) a. C. 3 R(NH3); é RrNHa b. d. é Rama); 2 RrNHa Q6A (15 pts.) Indicate which of the following plots would be obtained for a zeroth—order reaction. a. C. EMA] in[ t (sec) {{sec) EMA] ln[A] 1 (sec) 1 ' t (sec) Q6B (20 pts.) The following energy profiles for four different reactions are shown. Which of the reactions will have the greatest rate? Energy Energy Reacticn path Reaction path I 'Wfieacticn pathmfl H ' “Reaction path I c d STD: 0‘9? Q. Q. Q6C (15 pts.) The second-order reaction A + B ——> C will obey pseudo first—order kinetics when a. the concentrations of A and B are both small. the concentration of one of the reactants does not change. the concentration of C is large. the concentrations of A and B are both large. P-PF" Q7A (Bonus) (15 pts.) A proposed mechanism for the photodecomposition of ozone in the stratosphere is Step 1: 02(g) + hv —> 0(g) + 0(g) Step 21 0(g) + 02(g) + M(g) —> 0303) + M*(g) Step 3: 03(g) + hv —> 02(g) + 0(g) Step 41 0(g) + 0(8) + M(g) —> 02(g) + M*(g) where M is some other gas molecule (or atom) and M* indicates that M has been excited by a collision. What is the molecularity of Step 4? a. c. termolecular unimolecular b. bimolecular d. unable to determine Q7B (Bonus) (15 pts.) The steps in a reaction mechanism are as follows. Which species is acting as a catalyst? Step 1: Ag+(aq) + Ce4+(aq) <—-> T13+(aq) + Ce3+(aq) Step 2: T1+(aq) + AgZYaq) ~+ T12+(aq) + Ag+(aq) Step 3: TlZl"(aq) + Ce4+(aq) ~> Tl3+(aq) + Ce3+(aq) a. Ag 0. Ce3+ b. T1+ d. Ag2+ ...
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