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4:011 CHEM PRINCIPLES OF CHEMISTRY I EXAM #2 (30 QUESTIONS, 1 HOURS) 13-October-2005 FORM A 1. Calculate H for the reaction, N2O(g) + NO2(g) 3NO(g), using Hess's law and the following data: N2(g) + O2(g) 2NO(g) 2NO(g) + O2(g) 2NO2(g) 2N2O(g) 2N2(g) + O2(g) (A) (B) (C) (D) (E) +246.0 kJ -95.6 kJ +155.6 kJ +130.6 kJ -276.3 kJ H = +180.7 kJ H = -113.1 kJ H = -163.2 kJ 2. Phosgene decomposes according to the reaction, COCl2(g ) CO(g) + Cl2(g) where Kp = 0.0431 at a certain temperature. A pressure of 0.75 atm of COCl2 is introduced into a container and allowed to come to equilibrium. What is the partial pressure of CO(g) at equilibrium? (A) (B) (C) (D) (E) 3. 0.043 atm 0.16 atm 0.21 atm 0.32 atm 0.75 atm One million molecules of each of the following gases are simultaneously injected into the atmosphere at the back of a room. For which gas will the greatest amount of time lapse before 100 of its molecules will have struck the wall at the front of the room? (A) (B) (C) (D) (E) Cl2 CH4 NO2 CO2 NH3 4. Of the following, which one is impossible for an ideal gas? (A) (B) (C) (D) (E) V1/ T1 = V2/ T2 V1T1 = V2T2 V1/ V2 = T1/ T2 V2 = T2V1/ T1 V1/ V2 = P2/ P1 5. Cold packs, whose temperatures are lowered when ammonium nitrate dissolves in water, are carried by athletic trainers when transporting ice is not possible. Which of the following is true of this reaction? (A) (B) (C) (D) (E) H < 0, process is exothermic H > 0, process is exothermic H < 0, process is endothermic H > 0, process is endothermic H = 0, since cold packs are sealed 6. If a cubic centimeter of gas at 25C contains exactly one million molecules, what is the pressure of this gas in torr? ( R = 0.08206 Latm/molK ) (A) (B) (C) (D) (E) 2.59 10 torr 13 1.86 10 torr -14 4.06 10 torr -11 3.09 10 torr -14 3.09 10 torr -12 7. Consider the following equilibrium: 2 SO2(g) + O2(g) 2 SO3(g) The chemical equilibrium cannot be established when ______ is/are placed in a 1.0 L container: (A) (B) (C) (D) (E) 0.25 mol SO2(g) and 0.25 mol of O2(g) 0.25 mol SO2(g) and 0.25 mol of SO3(g) 0.50 mol O2(g) and 0.50 mol of SO3(g) 0.75 mol SO2(g) 1.0 mol SO3(g) 8. At times liquids other than mercury are used in manometers. Di-n-octyl phthalate was used in a closed-end manometer and the observed h was 5.68 cm. Assuming the vapor pressure of this phthalate is negligible, and the densities of mercury and di-n-octyl phthalate are 13.55 and 0.984 g/mL, respectively, what was the pressure of the gas being measured? (A) (B) (C) (D) (E) 78.2 torr 782 torr 56.8 torr 0.412 torr 4.12 torr 9. Which one of the following will result in a shift in the equilibrium position to the right? C(s) + H2O(g) CO(g) + H2(g) Hrxn = +131 kJ (A) (B) (C) (D) (E) Adding additional carbon Adding a substance that absorbs water Adding a catalyst Reducing the temperature (with the total pressure held constant) None of the above 10. Using an EDTA-titration method, a group of students measured the water hardness of samples prepared by passing tap water through a Brita water filter. Before passing through the filter, a 50. mL sample of the tap water required 14.98 mL of EDTA solution to reach the end point. Results for the titration of several 50. mL samples of Brita filtered water samples are displayed on the graph below. Titration Results for 50 mL Samples of Brita-Filtered Water 20 15 10 5 0 0 5 10 15 20 25 30 35 Total Volume of Tap Water Through Filter (L) 40 Approximately what fraction of the water hardness would removed from a 50. mL sample collected after 10.0 L of tap water has passed through the Brita filter? (A) (B) (C) (D) (E) /4 /3 1 /2 2 /3 cannot be determined without knowing the concentration of EDTA. 1 1 11. Each of the compounds listed below has the same molecular formula, C6H12O. Based on the heats of formation, for which compound is the combustion reaction most exothermic? (A) (B) (C) (D) (E) methyl isobutyl ketone, Hf = -291.2 kJ/mol cyclohexanol, Hf = -286.8 kJ/mol 1-methyl cyclopentanol, Hf = -284.3 kJ/mol 3-hexanone, Hf = -278.3 kJ/mol butyl vinyl ether, Hf = -179.2 kJ/mol 12. A student titrated a sample of a calcium standard with an EDTA solution and recorded the following data in her laboratory notebook: Initial buret reading = 1.57 mL Final buret reading = 15.86 mL [EDTA] = 0.0330 mol/L Volume of calcium standard = 50.00 mL Density of water 1.00 g/mL, Molar Mass CaCO3 = 100. g/mol 2+ 42Ca (aq) + EDTA (aq) [Ca EDTA] (aq) How many moles of Ca (A) (B) (C) (D) (E) 5.18 10 -4 4.72 10 -4 5.23 10 -2 5.23 10 -1 5.18 10 -5 2+ ions are in the sample that was titrated? 13. The heat of combustion of hydrogen gas is -242 kJ/mol. This is substantially less than the heat of combustion for methane, CH4, which is -802 kJ/mol. How many grams of hydrogen are required to produce the same amount of heat as 1.00 kg of CH4? (A) (B) (C) (D) (E) 414 g 725 g 1000 g 1414 g 3314 g 14. If the equilibrium constant for the reaction, 3O2(g) 2O3(g), is equal to K, the equilibrium constant for the reaction, O3(g) 3/2 O2(g), will be (A) (B) (C) (D) (E) (1/K) 3/2 (1/K) (3/2) (1/K) 1/2 (1/K) (1/2) (1/K) 15. Which of the following has (have) a standard heat of formation (Hf) of zero? (A) (B) (C) (D) (E) Ne(g) F(g) O(g) N(g) All of the above since they are all pure elements 16. An unknown volume of N2 gas and 20 mL of O2 gas are combined and allowed to react according to the following chemical equations, N2 + 2 O2 2 NO2 2 NO2 N2O4 The temperature and pressure of the mixture are held constant, and the volume of gas after the reaction is 30 mL. Assuming the reactions go to completion, what was the initial volume of N2 gas? (A) (B) (C) (D) (E) 0 mL 10 mL 20 mL 30 mL 40 mL 17. The Starship Enterprise is caught in a time warp and Spock is forced to use the primitive techniques of the 20th century to determine the specific heat capacity of an unknown mineral. The 307 g sample was heated to 98.7C and placed into calorimeter a containing 72.4 g of water at 23.6C. The heat capacity of the calorimeter was 15.7 J/K. The final temperature in the calorimeter was 32.4C. What is the specific heat capacity of the mineral? ( c of water is 4.184 J/gK). (A) (B) (C) (D) (E) 0.10 J/(gK) 0.17 J/(gK) 0.14 J/(gK) 0.19 J/(gK) 0.07 J/(gK) 18. BrCl is a binary interhalogen compound. At a certain temperature 12% of its molecules react to form bromine and chlorine, and equilibrium results, 2BrCl(g) Br2(g) + Cl2(g). What is the equilibrium constant, Kp, for this reaction under these conditions? (A) (B) (C) (D) (E) 0.0046 0.019 0.068 0.14 Kp cannot be calculated without knowing the initial pressure of BrCl. 19. The following reaction is at equilibrium in a sealed container. N2(g) + 3 H2(g) 2 NH3(g) Hrxn < 0 Which, if any, of the following actions will increase the value of the equilibrium constant, Kc? (A) (B) (C) (D) (E) decreasing the total pressure adding more N2 increasing the total pressure lowering the temperature removing NH3 20. Which one of the following statements is not correct at equilibrium? (A) (B) (C) (D) (E) The concentrations of reactants and products do not change. The reactants stop forming products. The concentrations of reactants and products depend on the temperature. The reaction quotient is equal to the equilibrium constant. All of the above statements are true at equilibrium. 21. An industrial chemist needs to get a 55 gallon drum of a nonvolatile liquid up to the rooftop of a building, but the building has no elevator and the drum is too heavy to carry. She decides to suck the liquid up a tube using a mechanical vacuum pump. If the prevailing atmospheric pressure is 29.6 in. Hg, what is the limit on the height of the building for this approach to work? ( d of Hg = 13.5 g/mL and d of the liquid = 1.50 g/mL ) (A) (B) (C) (D) (E) 3.29 in. 29.6 in. 22.2 ft 33.3 ft There is no limit on the height as long as she uses a big enough pump. 22. A student is in lab measuring the constant pressure heat of reaction for the neutralization of hydrochloric acid by sodium hydroxide. The lab manual says to use 100 mL of 0.500 M NaOH and 100 mL of 0.500 M HCl. The student was in a hurry and misread the lab manual and used half the volume of each of the solutions. What result will the student measure compared to what they would have measured without the mistake assuming an ideal calorimeter that absorbs no heat? (A) (B) (C) (D) (E) The temperature change will be half as large. The temperature change will be two times larger. The temperature change will be one fourth as large. The temperature change will be four times larger. The temperature change will be exactly the same. 23. Drew Tate weighs 185 lbs, and from this weight it can be estimated that he burns 614 Calories for every hour of football played. Given the time played indicated below, in which game did he burn the approximate number of Calories contained in a package of M&Ms (236 Calories/package)? (A) (B) (C) (D) (E) Ball State, time played ~31 min Iowa State, time played ~23 min Northern Iowa, time played ~26 min Ohio State, time played ~21 min Illinois, time played ~29 min 24. The gas in a balloon performed 0.300 kJ of work while expanding. At the same time the gas absorbed 50. J of heat. The change in internal energy (E) of this gas is, (A) (B) (C) (D) (E) +350. J -250. J -350. J +250. J 50. J 25. A person inhales air rich in O2 and exhales air rich in CO2. During each hour of sleep, a person exhales a total of about 300. L of air. The partial pressure of CO2 in exhaled air is 30.0 torr at 37.0C. Assuming all of the CO2 comes from the metabolism of glucose with the equation, C6H12O6 + 6 O2 6 CO2 + 6 H2O How many grams of body mass does the person lose in 8 hours of sleep? (A) (B) (C) (D) (E) 14.0 g 28.8 g 112 g 231 g 670. g 26. An important step in the synthesis of nitric acid is the conversion of ammonia to nitric oxide. Hf [NH3(g)] = -45.9 kJ/mol; Hf [NO(g)] = 90.3 kJ/mol; Hf [H2O(g)] = -241.8 kJ/mol 4 NH3(g) + 5 O2(g) 4 NO(g) + 6 H2O(g) Calculate Hrxn for this reaction. (A) (B) (C) (D) (E) -906. kJ -197.4 kJ -105.6 kJ 197.4 kJ 906. kJ 27. At a pressure of 200 atm the measured pressure exerted by CO2 gas is less than that predicted by the ideal gas equation. This is mainly because: (A) such high pressures cannot be accurately measured. (B) ideal gas molecules would collide with the walls of the container less frequently than CO2 molecules. (C) gas phase collisions prevent CO2 molecules from colliding with the walls of the container. (D) of attractive intermolecular forces between CO2 molecules. (E) the volume occupied by the CO2 molecules themselves becomes significant. 28. A compound composed of carbon, hydrogen, and chlorine effuses through a pinhole 0.411 times as fast as neon. Which of the following compounds has a formula weight consistent with this behavior? (A) (B) (C) (D) (E) CHCl3 CH2Cl2 C2H2Cl2 C2H3Cl CCl4 29. The equilibrium constant, Kp, for the reaction H2(g) + I2(g) 2HI(g) is 55.2 at 425C. A rigid cylinder at that temperature contains 0.127 atm of hydrogen, 0.134 atm of iodine, and 1.055 atm of hydrogen iodide. Is the system at equilibrium? (A) No, the forward reaction must proceed to establish equilibrium. (B) Cannot be determined. Need to know the volume of the container before deciding. (C) No, the reverse reaction must proceed to establish equilibrium. (D) Yes. (E) Cannot be determined. Need to know the starting concentrations of all substances before deciding. 30. Calculate Kc for the following reaction, 2 H2(g) + C(s) (A) (B) (C) (D) (E) 3.15x10 -3 3.19x10 0.262 21.5 2180 -5 CH4(g) Kp = 0.262 at 1000. K Exam #2 Fall 2005 KEY Chem 004:011 Principles of Chemistry I Eyman / Hansen / Cheatum / Larsen Question 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 Answer C B A B D D D E E B E B A D A D C A D B C E B B C A D A C D ... View Full Document

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