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Unformatted text preview: CHM-102 NAME • • • • • • • Key Exam I I Form A Summer 2010 Raw Score T-Score You will have 70 minutes to complete the exam. There is one best answer to each question and all questions are worth the same number of points. Sign your name on the answer sheet above the General Purpose logo on the front. Write the form of the test you are taking next to your name. Print and fill in your name (last name-space-first name) on the back of your answer sheet. Be sure to mark the correct answers on your exam booklet so you can compare your answers to the answer key. An answer key will be posted immediately following the test at the course website as well as outside DO-236. 1. What amount of thermal energy (Q) is given off when 10 g of water, initially at 10 oC, are converted to ice at 0 oC? [The specific heat of water (C) is 4.18 J/g·K and ΔHfus = 6.01 kJ/mol] a. 6.3 x 103 J b. 1.2 x 103 J c. 3.8 x 103 J d. 421 J 2. Shown below is the heating curve for a substance. Which of the following statements is correct? 3 4 1 2 a) The segment 1 – 2 corresponds to ΔHfusion b) The segment 2 – 3 corresponds to the specific heat of the substance as a liquid. c) The segment 3 – 4 corresponds to ΔHvaporization d) All of the statements are correct. Page 1 of 9 3. Imagine that you have a stoppered 125 mL Erlenmeyer flask that contains 20 mL of water at 25 ºC. In which of the flasks pictured below is the vapor pressure of water the same as in the original flask? a. i and iii only 4. b. iii only c. i only d. i, ii, and iii Based on the graph given below, what is the approximate boiling point of ethanol at 0.45 atm pressure? a. 80 °C b. 20 °C c. 40 °C d. 60 °C 5. Iron metal crystallizes with a body-centered-cubic unit cell. The unit cell edge length is 323 pm. What is the radius (in pm) of an iron atom? a. 140 pm b. 162 pm c. 114 pm d. 746 pm Page 2 of 9 The phase diagram shown below is used to answer questions 6 and 7. 6. The point marked by the arrow “z” in the phase diagram is the a. triple point c. normal melting point b. critical point d. normal boiling point 7. The region “w” corresponds to the: a. Gas phase b. Critical point c. Liquid phase d. Solid phase 8. Some ionic compounds crystallize in what is called the fluorite structure. In this structure, the cations (X) form a facecentered-cubic (fcc) array and the anions (Y) occupy the eight tetrahedral holes inside the fcc array. What is the general formula for an ionic compound that crystallizes using the fluorite structure? a. XY c. XY2 9. d. X7Y4 b. X2Y _________ solids consist of atoms or molecules held together by dipole-dipole forces, London disperson forces, and/or hydrogen bonds. b. Covalent-network c. Metallic d. Molecular a. Ionic 10. Which of the following liquids is immiscible with water? a. a. Methanol b. acetone c. hexane d. acetonitrile Page 3 of 9 11. The Henry’s law constant for N2(g) at 25 °C is 6.40 x 10-4 M atm-1. What mass (in g) of N2(g) will dissolve in 1000 mL of aqueous solution if the pressure of N2 gas is 0.800 atm? a. 2.05 x 10-3 g b. 5.12 x 10-4 g c. 5.12 x 10-3 g d. 1.43 x 10-2 g 12. Determine the molarity of a solution prepared by dissolving 5.5 g of HCl in 200 g of C2H6O if the density of the resulting solution is 0.79 g/mL. a. 21 M b. 0.93 M c. 0.58 M d. 1.72 M 13. What is the mole fraction of urea (MW = 60) in a solution prepared by dissolving 16 g of urea in 39 g of water (MW = 18) assuming the density of the resulting solution is 1.2 g/mL? a. 0.58 b. 0.37 c. 0.13 d. 0.11 14. Which one of the following solutions will have the highest boiling point? a. 0.25 m C6H12O6 (glucose) c. 0.75 m CH3OH b. 0.10 m Na3PO4 d. 0.40 m CaCl2 15. An aqueous solution of KCl boils at 102 oC. What is the freezing point of this solution? (Kb for water = 0.512 ºC/m; Kf for water = 1.86 ºC/m) a. -7.3 oC b. -2.0 oC c. -3.6 oC d. -14 oC Page 4 of 9 16. Which of the reactions below is consistent with the following concentration profiles for reactant and products? a. 2 NO3(g) b. 2 H2O2(l) c. 2 N2O5(g) d. 2 NaClO3(s) 2 NO2(g) + O2(g) 2 H2O(l) + O2(g) 4 NO2(g) + O2(g) 2 NaCl(s) + 3 O2(g) 17. The following experimental data were collected for the reaction 2A +3B Experiment # 1 2 3 4 Reactant A (M) 0.15 0.32 0.45 0.15 products Reactant B (M) 0.15 0.53 0.15 0.30 Initial rate (M/s) 1.2 x 10-2 2.6 x 10-2 3.6 x 10-2 1.2 x 10-2 What is the rate law for the reaction? a. rate = k [A]2[B]3 c. rate = k [A][B] b. rate = k [A][B]2 d. rate = k [A] Page 5 of 9 Use the following data for a first-order reaction to answer questions 18 to 20. Time (s) 2 4 6 8 10 12 Reactant (M) 4.24 3.00 2.12 1.50 1.06 0.75 18. What is the average reaction rate between 6 and 10s? a. 1.06 Ms-1 b. 0.265 Ms-1 c. 3.77 Ms-1 d. 0.530 Ms-1 19. What is the half-time (t1/2) for the reaction? a. 4.00 s b. 8.00 s c. 1.81 s d. 6.00 s 20. What is the rate constant (k) for the reaction? a. 2.77 s b. 5.77 s-1 c. 5.77 s d. 0.173 s-1 21. Methanol reacts with oxygen according to the following balanced equation. 2 CH3OH(aq) + 3 O2(g) 2 CO2(g) + 4 H2O(g) Increasing which of the following would be most effective in increasing the rate of the reaction? a. b. c. d. the concentration of CH3OH the partial pressure of O2 the concentration of CO2 insufficient information to answer the question Page 6 of 9 22. The following data were collected for a first-order reaction. What was the concentration of reactant at t = 0? a. 9.0 M b. 8.0 M c. 7.0 M d. 6.0 M 23. At elevated temperatures, nitrogen dioxide decomposes to nitrogen oxide and oxygen:
NO 2 (g) → NO (g) + 1 O 2 (g) 2 The reaction is second order in NO2 with a rate constant of 0.543 M-1s-1 at 300 °C. What would happen if the temperature were raised to 450 °C? A. B. C. D. The rate constant for the reaction will increase. The activation energy for the reaction will increase. Nothing, because monomolecular reactions are independent of temperature. The reaction will become endothermic. Page 7 of 9 Important Formulas and Constants
P1V1 P2V2 = n1T1 n 2 T2 PV = nRT PV = mRT M PT = P1 + P2 + P3 + ... Xa = na nT Pa = X a PT r1 = r2 M2 M1 Q = ΔH vap mol Q = ΔH fusion mol Q = CmΔT R = 0.0821 L·atm·K-1·mol-1 K = ºC + 273 1 atm = 760 mmHg = 760 torr = 101.3 kPa For sc: 2r = a
M= moles solute Lsolution For fcc: 4r = a 2
0 PA = χ A PA For bcc: 4r = a 3
ppm = mg solute kg solution ppb = moles solute kg solvent μg solute
kg solution S g = kPg Rate = − Δ[ A] Δt ΔTb = iK b m ΔT f = −iK f m
ln[ A] = −kt + ln[ A]0 Rate = k[ A] m [ B ] n
− Ea t1 / 2 = 0.693 k k = Ae RT Page 8 of 9 Scratch paper Page 9 of 9 ...
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- Summer '09