CHEM Exam 3 November 2, Version A. Constants: NA = 6.02x10 23 mol -1 R = L atm/mol K R = 8.31 J/mol K

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1 CHEM Exam 3 November 2, Version A Molar Masses: Mn KClO SO Cl2-71. CO2-44. C2H6-30. NH3-17. H2O C6H Na AgNO C10H Conversions: 1 atm = 760 torr 1 L atm = 101 J 1 L = 1.06 Qt Constants: NA = 6.02x10 23 mol -1 R = L atm/mol K R = 8.31 J/mol K

2 CHEM Exam 3 November 2, Version A (76) MULTIPLE CHOICE (Circle the ONE correct answer) Name 1. How many molecules are there in a sample of a gas at 1000 torr and 250 o C in a 20 L container? (A) 2.8x10 22 (B) 3.7x10 23 (C) 7.7x10 23 (D) 2.8x The temperature of a gas at a pressure of 400 torr and volume of 40 L is 200 o C. What is the temperature of the gas, in o C, at a pressure of 500 torr and volume of 30 L? (A) 170 o C (B) 188 o C (C) 124 o C (D) 82 o C 3. An unknown gas has a density of 2.80 g/l at a temperature of 25 o C and pressure of 0.80 atm. What is the approximate Molar Mass of the gas? (A) 39 g/mol (B) 114 g/mol (C) 62 g/mol (D) 86 g/mol 4. The fraction of Xe(g) in air is 450 ppb (parts per billion). What is the partial pressure of Xe(g), in torr, when the total air pressure of 0.90 atm.? (A) 4.1x10-7 torr (B) 3.1x10-4 torr (C) 2.7x10-1 torr (D) 3.1x10-1 torr 5. A mixture contains 0.40 moles of N2(g) and 1.20 moles of O2(g). The partial pressure of N2 is 150 torr. Therefore, the partial pressure of O2 is torr and the total pressure is torr. (A) 450, 600 (B) 600, 750 (C) 600, 450 (D) 300, Dimanganese decacarbonyl, Mn2(CO)10(s), can be made by the reaction of Mn(s) with CO(g). Approximately how many grams of Mn(s) are required to react completely 1200 L of CO(g) at 100 o C and a pressure of 500 torr to produce Mn2(CO)10(s)? (A) 140 g (B) 280 g (C) 1420 g (D) None of the above 7. Consider the reaction, N2(g) + O2(g) N2O5(g). Approximately how many moles of N2O5 can be produced by the reaction of 60 L of N2(g) at 400 K and 1. atm. with 130 L of O2(g) at 400 K and 1. atm? (A) 1.83 mol (B) 3.96 mol (C) 1.32 mol (D) 1.58 mol

3 Version A 8. When heat is applied to potassium chlorate, KClO3(s), it decomposes to potassium chloride, KCl(s), and oxygen, O2(g). When a sample of KClO3 is heated to 250 o C, it decomposes to produce 460 L of O2(g) at 250 o C and 0.90 atm. Approximately how many grams of KClO3(s) decomposed? (A) 790 g (B) 1180 g (C) 1650 g (D) 1780 g 9. The RMS average speed of SO2(g) molecules at 25 o C is 340 m/s. What is the RMS average speed of SO2(g) molecules at 800 o C? (A) 1920 m/s (B) 180 m/s (C) 1220 m/s (D) 645 m/s 10. Consider the following 3 gases: (i) Cl2(g) at 150 o C, (ii) CO2(g) at 180 o C, (iii) C2H6(g) at 150 o C. has the lowest rate of effusion and has the highest Kinetic Energy. (A) CO2, Cl2 (B) Cl2, CO2 (C) C2H6, CO2 (D) Cl2, C2H6 11. It takes 45 seconds for a sample of SO2(g) to effuse through a pinhole. Under the same conditions it takes 60 seconds for an equivalent sample of an unknown gas to effuse through the pinhole. Therefore, the Molar Mass of the unknown gas is: (A) 85 g/mol (B) 74 g/mol (C) 114 g/mol (D) 36 g/mol 12. The compressibility of a gas, PV/RT, represents the deviation from Ideal Gas behavior. If the compressibility is greater than 1, i.e. PV/RT > 1, then: (i) Attractive Forces predominate (ii) Repulsive Forces predominate (iii) The gas is less compressibile than an Ideal Gas (iv) The gas is more compressibile than an Ideal Gas (A) i & iv (B) ii & iii (C) i & iii (D) ii & iv 13. For which of the following processes is the work positive (w>0)? (i) A gas is cooled at constant pressure (ii) C6H6(l) C6H6(g) (iii) A gas is cooled at constant volume (iv) N2(g) + 3 H2(g) 2 NH3(g) (A) i & iv (B) i & ii (C) i & iii & iv (D) iv only 14. The constant pressure molar heat capacity of NH3(g) is 37. J/mol- o C. When 8. kj of heat is added (at constant pressure) to a sample of 40 g of NH3(g) originally at 30 o C, what is the final temperature of the sample? (A) 104 o C (B) 92 o C (C) 163 o C (D) 122 o C

4 Version A 15. When a sample of a gas is cooled from 300 o C to 100 o C at a constant pressure of 2,000 torr, the volume changes from 120 Qt. to 75 Qt.. What is the approximate value of the work (w) for this process (in kj)? (A) kj (B) kj (C) kj (D) kj For #16 - #17: Consider the following reaction: 2 C6H14(l) + 19 O2(g) 12 CO2(g) + 14 H2O(l) H = kj 16. If C6H14 reacts with O2, and 12,000. kj of heat is released, approximately how many grams of H2O(l) have been produced? (A) 360 g (B) 175 g (C) 470 g (D) 26 g 17. What is the approximate heat involved in the production of 40 g of C6H14(l) from CO2(g) and H2O(l)? (A) kj (B) kj (C) kj (D) kj 18. Consider the reaction of sodium with water: 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) H o = -240 kj The Enthalpy of Fusion of water is 6.0 kj/mol. When 40 grams of Na(s) is dropped in a container containing ice and liquid water at 0 o C, approximately how many grams of ice will melt? (A) 830 g (B) 630 g (C) 1250 g (D) 470 g 19. In an experiment to determine the Enthalpy of Solution of AgNO3, 20. grams of AgNO3(s) was dissolved in 100 grams of water at 28.0 o C. It was found that the temperature in the solution cooled to 21.7 o C. The Heat Capacity of the solution was Csoln = 420 J/ o C. Therefore, the Heat of Solution of AgNO3 is approximately: (A) kj (B) kj (C) kj (D) None of the above Two (2) Problems Follow (You MUST show your work to receive credit)

5 Version A (12) 1. A hypothetical element, X(s), reacts with O2(g) to form X3O4(s). It is found that 20. grams of X require 8.10 L of O2 at 30 o C and 700. torr to react completely. Calculate the Molar Mass of the element, X? (12) 2. Use the data below on a 320 gram sample of Napthalene, C10H8, to calculate the heat involved, in kilojoules (kj) for the process below: C10H8(gas, 218 o C) C10H8(solid, 80 o C) at a constant pressure of 1 atm. C5H8 Data M = 128. g/mol Tm = 80 o C Tb = 218 o C Hfus= 19. kj/mol Hvap = 55. kj/mol Cp,m(liq) = 196 J/mol- o C

6 CHEM Exam 3 November 2, Version B Molar Masses: Mn KClO SO Cl2-71. CO2-44. C2H6-30. NH3-17. H2O C6H Na AgNO C10H Conversions: 1 atm = 760 torr 1 L atm = 101 J 1 L = 1.06 Qt Constants: NA = 6.02x10 23 mol -1 R = L atm/mol K R = 8.31 J/mol K

7 CHEM Exam 3 November 2, Version B (76) MULTIPLE CHOICE (Circle the ONE correct answer) Name 1. The temperature of a gas at a pressure of 400 torr and volume of 40 L is 200 o C. What is the temperature of the gas, in o C, at a pressure of 500 torr and volume of 30 L? (A) 124 o C (B) 188 o C (C) 170 o C (D) 82 o C 2. How many molecules are there in a sample of a gas at 1000 torr and 250 o C in a 20 L container? (A) 2.8x10 22 (B) 7.7x10 23 (C) 2.8x10 23 (D) 3.7x The fraction of Xe(g) in air is 450 ppb (parts per billion). What is the partial pressure of Xe(g), in torr, when the total air pressure of 0.90 atm.? (A) 3.1x10-4 torr (B) 4.1x10-7 torr (C) 2.7x10-1 torr (D) 3.1x10-1 torr 4. A mixture contains 0.40 moles of N2(g) and 1.20 moles of O2(g). The partial pressure of N2 is 150 torr. Therefore, the partial pressure of O2 is torr and the total pressure is torr. (A) 600, 450 (B) 600, 750 (C) 450, 600 (D) 300, An unknown gas has a density of 2.80 g/l at a temperature of 25 o C and pressure of 0.80 atm. What is the approximate Molar Mass of the gas? (A) 39 g/mol (B) 86 g/mol (C) 62 g/mol (D) 114 g/mol 6. Consider the reaction, N2(g) + O2(g) N2O5(g). Approximately how many moles of N2O5 can be produced by the reaction of 60 L of N2(g) at 400 K and 1. atm. with 130 L of O2(g) at 400 K and 1. atm? (A) 1.83 mol (B) 3.96 mol (C) 1.58 mol (D) 1.32 mol 7. Dimanganese decacarbonyl, Mn2(CO)10(s), can be made by the reaction of Mn(s) with CO(g). Approximately how many grams of Mn(s) are required to react completely 1200 L of CO(g) at 100 o C and a pressure of 500 torr to produce Mn2(CO)10(s)? (A) 280 g (B) 140 g (C) 1420 g (D) None of the above

8 Version B 8. The RMS average speed of SO2(g) molecules at 25 o C is 340 m/s. What is the RMS average speed of SO2(g) molecules at 800 o C? (A) 1920 m/s (B) 645 m/s (C) 1220 m/s (D) 180 m/s 9. When heat is applied to potassium chlorate, KClO3(s), it decomposes to potassium chloride, KCl(s), and oxygen, O2(g). When a sample of KClO3 is heated to 250 o C, it decomposes to produce 460 L of O2(g) at 250 o C and 0.90 atm. Approximately how many grams of KClO3(s) decomposed? (A) 1780 g (B) 1180 g (C) 1650 g (D) 790 g 10. It takes 45 seconds for a sample of SO2(g) to effuse through a pinhole. Under the same conditions it takes 60 seconds for an equivalent sample of an unknown gas to effuse through the pinhole. Therefore, the Molar Mass of the unknown gas is: (A) 85 g/mol (B) 114 g/mol (C) 74 g/mol (D) 36 g/mol 11. Consider the following 3 gases: (i) Cl2(g) at 150 o C, (ii) CO2(g) at 180 o C, (iii) C2H6(g) at 150 o C. has the lowest rate of effusion and has the highest Kinetic Energy. (A) Cl2, CO2 (B) CO2, Cl2 (C) C2H6, CO2 (D) Cl2, C2H6 12. The compressibility of a gas, PV/RT, represents the deviation from Ideal Gas behavior. If the compressibility is greater than 1, i.e. PV/RT > 1, then: (i) Attractive Forces predominate (ii) Repulsive Forces predominate (iii) The gas is less compressibile than an Ideal Gas (iv) The gas is more compressibile than an Ideal Gas (A) i & iv (B) ii & iv (C) i & iii (D) ii & iii 13. The constant pressure molar heat capacity of NH3(g) is 37. J/mol- o C. When 8. kj of heat is added (at constant pressure) to a sample of 40 g of NH3(g) originally at 30 o C, what is the final temperature of the sample? (A) 104 o C (B) 92 o C (C) 122 o C (D) 163 o C 14. For which of the following processes is the work positive (w>0)? (i) A gas is cooled at constant pressure (ii) C6H6(l) C6H6(g) (iii) A gas is cooled at constant volume (iv) N2(g) + 3 H2(g) 2 NH3(g) (A) i & ii (B) i & iv (C) i & iii & iv (D) iv only

9 Version B For #15 - #16: Consider the following reaction: 2 C6H14(l) + 19 O2(g) 12 CO2(g) + 14 H2O(l) H = kj 15. If C6H14 reacts with O2, and 12,000. kj of heat is released, approximately how many grams of H2O(l) have been produced? (A) 360 g (B) 26 g (C) 470 g (D) 175 g 16. What is the approximate heat involved in the production of 40 g of C6H14(l) from CO2(g) and H2O(l)? (A) kj (B) kj (C) kj (D) kj 17. When a sample of a gas is cooled from 300 o C to 100 o C at a constant pressure of 2,000 torr, the volume changes from 120 Qt. to 75 Qt.. What is the approximate value of the work (w) for this process (in kj)? (A) kj (B) kj (C) kj (D) kj 18. In an experiment to determine the Enthalpy of Solution of AgNO3, 20. grams of AgNO3(s) was dissolved in 100 grams of water at 28.0 o C. It was found that the temperature in the solution cooled to 21.7 o C. The Heat Capacity of the solution was Csoln = 420 J/ o C. Therefore, the Heat of Solution of AgNO3 is approximately: (A) kj (B) kj (C) kj (D) None of the above 19. Consider the reaction of sodium with water: 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) H o = -240 kj The Enthalpy of Fusion of water is 6.0 kj/mol. When 40 grams of Na(s) is dropped in a container containing ice and liquid water at 0 o C, approximately how many grams of ice will melt? (A) 830 g (B) 470 g (C) 1250 g (D) 630 g Two (2) Problems Follow (You MUST show your work to receive credit)

10 Version B (12) 1. A hypothetical element, X(s), reacts with O2(g) to form X3O4(s). It is found that 20. grams of X require 7.60 L of O2 at 30 o C and 700. torr to react completely. Calculate the Molar Mass of the element, X? (12) 2. Use the data below on a 384. gram sample of Napthalene, C10H8, to calculate the heat involved, in kilojoules (kj) for the process below: C10H8(gas, 218 o C) C10H8(solid, 80 o C) at a constant pressure of 1 atm. C5H8 Data M = 128. g/mol Tm = 80 o C Tb = 218 o C Hfus= 19. kj/mol Hvap = 55. kj/mol Cp,m(liq) = 196 J/mol- o C

Ch 9 Practice Problems

Ch 9 Practice Problems 1. One mole of an ideal gas is expanded from a volume of 1.50 L to a volume of 10.18 L against a constant external pressure of 1.03 atm. Calculate the work. (1 L atm = 101.3 J) A)