Practice Questions For The Last Part Of The Material PDF

Practice Questions for the last part of the material CHEM 101 Potentially useful data: 23 -1 Avogadro’s constant: 6.022 × 10 mol -1 -1 R = 0.0821 L∙atm∙mol ∙K 1 atm = 14.7 psi 1 atm = 760 mm H...

Practice Questions for the last part of the material CHEM 101 Potentially useful data: 23 -1 Avogadro’s constant: 6.022 × 10 mol -1 -1 R = 0.0821 L∙atm∙mol ∙K 1 atm = 14.7 psi 1 atm = 760 mm Hg 1 atm = 760 mm torr o 0 C = 273.15 K pV = nRT 1. A sample of gas occupies 10.2 L at 1 atm and 0 °C. Estimate the temperature (in °C) at which the same gas will occupy 15,000 mL at 1550 torr. a. -273 °C b. 1.22 × 10 -3 °C c. 546 °C d. 6.22 × 10 5 °C e. 0 °C 2. A 5.0 L container encloses N2, O2, and Ne at 1 atm and 0 °C. The mole fraction of N2 is 0.55 and the mole fraction of Ne is 0.25. Estimate the number of molecules of O2 present in the mixture. 22 a. 2.7 × 10 molecules O2 22 b. 4.5 × 10 molecules O2 23 c. 3.7 × 10 molecules O2 23 d. 1.1 × 10 molecules O2 24 e. 9.3 × 10 molecules O2 3. Which statement is FALSE? a) The air we exhale expands continuously into the atmosphere. b) If a large container is filled with a small amount of gas, the gas will occupy the whole container. c) Gas molecules cannot be squeezed together to fit into a very small container. d) The density of the liquid in a barometer is inversely proportional to the height of the liquid column. e) 73.5 psi = 5 atm. Page 1 of 5 4. A 1.44-g sample of an unknown pure gas occupies a volume of 0.335 L at a pressure of 1.00 atm and a temperature of 100 °C. The unknown gas is __________. a. Xe b. He c. Kr d. Ne e. Ar 5. If the pressure in a gas container connected to an open-end U-tube manometer is 1.145 atm and the pressure of the atmosphere at the open end of the tube is 752 mm Hg, the level of mercury in the tube will be about ________. a) 870 mm higher in the arm open to the atmosphere b) 118 mm higher in the arm connected to the gas cylinder c) 870 mm higher in the arm connected to the gas cylinder d) the same in both arms e) 118 mm Hg higher in the arm open to the atmosphere 6. Which of the following statements is NOT part of the kinetic molecular theory? a) Gas molecules have no significant volume. b) The average kinetic energy of gas molecules is directly proportional to the gas temperature. c) Collisions between gas particles are elastic. d) Each gaseous element is composed of atoms of the same mass. e) There is no electrostatic attraction or repulsion between gas molecules. o 7. A gas in a balloon occupies a volume of 2 L at 25 C. Upon heating, the balloon expands to a volume of 6 L. Estimate the new temperature (in K) of the gas in the balloon. a) 993 K b) 403 K c) 75 K d) 655 K e) 894 K 8. The internal pressure of 2.0 L of gas changes from 1.74 atm to 421.8 mm Hg at 25 oC. Estimate the resulting volume (in L) occupied by the gas at the same temperature. a) 0.48 L b) 0.64 L c) 1.9 L d) 6.3 L e) 20 L Page 6 of 5 9. Estimate the heat of reaction during the formation of 98.7 g of Fe, according to the thermochemical equation below. Fe2O3 (s) + 2 Al (s) → Al2O3 (s) + 2 Fe (s) ΔHrxn = - 852 kJ 3 a) - 3.01 × 10 kJ 3 b) - 1.51 × 10 kJ c) - 753 kJ 6 d) - 2.35 × 10 kJ e) - 241 kJ 10. At constant pressure, the temperature of a flask equipped with a moveable piston is reduced to half its original absolute temperature. Consequently, the volume of the air inside the flask becomes _______ the original volume. a) 1/4 b) 1/2 c) two times d) four times e) equal to 11. 12. A compound is found to be 30.45% N and 69.55 % O by mass. If 1.63 g of this compound occupy 389 mL at 0.00°C and 775 mm Hg, what is the molecular formula of the compound? A) NO2 B) N2O C) N4O2 D) N2O5 E) N2O4 Page 6 of 5 13. A syringe contains 589 mL of CO at 325 K and 1.2 atm pressure. A second syringe contains 473 mL of N2 at 298 K and 2.6 atm. What is the final pressure if the contents of these two syringes are injected into a 1.00 L container at 273 K? A) 0.59 atm B) 1.1 atm C) 1.7 atm D) 1.9 atm E) 3.8 atm 14. Determine the volume of O2 (at STP) formed when 50.0 g of KClO3 decomposes according to the following reaction. The molar mass for KClO3 is 122.55 g/mol. 2 KClO3(s) → 2 KCl(s) + 3 O2(g) A) 9.14 L B) 8.22 L C) 12.3 L D) 13.7 L E) 14.6 L 15. Determine the theoretical yield and the percent yield if 21.8 g of K2CO3 is produced from reacting 27.9 g KO2 with 29.0 L of CO2 (at STP). The molar mass of KO2 = 71.10 g/mol and K2CO3 = 138.21 g/mol. 4 KO2(s) + 2 CO2(g) → 2 K2CO3(s) + 3 O2(g) A) 27.1 g, 80.4 % yield B) 179 g, 12.2 % yield C) 91.7 g, 23.8 % yield D) 206 g, 10.6 % yield E) 61.0 g, 35.7 % yield 16. Determine the mass of water formed when 12.5 L NH3 (at 298 K and 1.50 atm) is reacted with 18.9 L of O2 (at 323 K and 1.1 atm). 4 NH3(g) + 5 O2(g) → 4 NO(g) + 6 H2O(g) A) 17.0 g H2O B) 20.7 g H2O C) 37.7 g H2O D) 13.8 g H2O E) 27.9 g H2O Page 6 of 5 17. If 2.0 moles of gas A are mixed with 1.0 mol of gas B to give a total pressure of 1.6 atm, what is the partial pressure of gas A and B? A) PA = 0.33 atm and PB = 0.67 atm B) PA = 0.67 atm and PB = 0.33 atm C) PA = 1.0 atm and PB = 2.0 atm D) PA = 2.0 atm and PB = 1.0 atm E) PA = 1.06 atm and PB = 0.53 atm 18. A sample of 1.58 g of an unknown gas has a volume of 0.682 L. The sample is kept at 60°C, and exerts a pressure of 1.38 atm. What is the gas? A) Cl2 B) NO C) NO2 D) SO2 E) C2H6 19. A sample of neon at 30.5°C exerts a pressure of 701 mm Hg. What is its density? A) 0.747 g/mL B) 563 g/mL C) 7.42 g/mL D) 1.38 g/mL E) 0.482 g/mL 20. A 4.00-L flask contains nitrogen gas at 25°C and 1.00 atm pressure. What is the final pressure in the flask if an additional 2.00 g of N2 gas is added to the flask and the flask cooled to -55°C? A) 0.319 atm B) 1.05 atm C) 1.44 atm D) 1.96 atm 21. Consider the thermochemical equation below. Which of the following statements is FALSE? N2 (g) + 3 H2 (g) → 2 NH3 (g) ΔHrxn = - 459.0 kJ a) The formation of 1.00 mole of NH3 releases 229.5 kJ of heat. b) The complete reaction of 0.8277 moles of H2 requires 0.2759 moles of N2. c) The complete reaction of 0.25 moles of N2 requires 114.75 kJ of heat. d) The decomposition of 1.00 mole of NH3 requires 229.5 kJ of heat. e) None. All of the above statements are true. Page 6 of 5 22. Using the thermochemical equation below, estimate the enthalpy change of reaction for the production of 4 moles of CO2 by the decomposition of solid barium carbonate, BaCO3. BaO (s) + CO2 (g) → BaCO3 (s) ∆Hrxn = - 662.8 kJ a) 662.8 kJ 3 b) 2.65 x 10 kJ c) - 2651 J d) 2651 J -3 e) 2.65 x 10 kJ 23. Which of the following describes an endothermic process? a) Chemical bonds form. b) The energy of all the bonds that break is greater than the energy of all the bonds that form. c) The energy of all the bonds that break is less than the energy of all the bonds that form. d) Strong bonds form and an equal number of weaker bonds break. e) None. All of the above are examples of exothermic reactions. 24. The value of ΔHrxn for the reaction illustrated by the chemical equation below is +128.1 kJ. Approximate the amount of heat (in kJ) that is consumed when 5.10 g of H2(g) form. CH3OH (l) → CO (g) + 2 H2 (g) a) 161.7 kJ b) 62.0 kJ c) 128.1 kJ d) 256.2 kJ e) 101.4 kJ 25. Estimate the heat of reaction, ∆Hrxn, for the process described by the following chemical equation Fe2O3 (s) + FeO (s) → Fe3O4 (s) based on the information given below: 2 Fe(s) + O2(g) → 2 FeO(s) ΔHrxn = - 544.0 kJ 4 Fe(s) + 3 O2(g) → 2 Fe2O3(s) ΔHrxn = - 1648.8 kJ 3 Fe(s) + 2 O2(g) → Fe3O4(s) ΔHrxn = - 1118.4 kJ a) - 1074.0 kJ b) - 22.0 kJ c) 22.2 kJ d) 249.8 kJ e) 1074.0 kJ Page 6 of 5 ANSWER KEY 1. c) 2. a) 3. c) 4. a) Recall that the number of moles is determined by dividing the mass by the molar mass. 5. e) 6. d) 7. e) Write the ideal gas law for the initial state of the gas, and then for the final state of the gas. Divide the two equations such that what stays constant will cancel out. Solve for T. 8. d) Same reasoning as for the previous question (question 7). 9. c) The balanced thermochemical equation indicates the 852 kJ released for 2 moles of Fe. Convert the mass of Fe to moles, and then set up a proportion to calculate the corresponding amount of heat (852 kJ/2 mol is your conversion factor). 10. b) Same reasoning as for questions 7 and 8. 11. e) 12. e) Use the ideal gas law equation to find out the molar mass of the compound (don't forget to convert o mL to L, C to K and mm Hg to atm before plugging in the corresponding numbers, since you have to match the units of measure for R). Then set up a proportion with the given %: if 30.45 g N in 100 g of compound, then how many grams of N in the molar mass that you calculated. The mass of N in g is the mass on N in one mole of compound. Divide it by the atomic mass to find out how many moles of N atoms per mole of compound. The molar ratio also indicates the atomic ratio in one molecule of that compound. 13. c) 14. d) 15. a) 16. a) 17. e) 18. c) 19. a) 20. b) 21. c) 22. b) 23. b) 24. a) 25. b) Page 6 of 5