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Question 1 1. Consider the following equilibrium: ½N2O4(g) NO2(g); Kc = 3.3 at 100°C For which of the following equilibria is Kc less than 3.3 at 100°C? Answer 2N2O4(g) N2O4(g) 4NO2(g) 2NO2(g) 4N2O4(g) 8NO2(g) 3N2O4(g) 6NO2(g) ¼N2O4(g) ½NO2(g) 6.7 points Question 2 1. For the reaction IO3–(aq) + 5I–(aq) + 6H+(aq) → 3I2(aq) + 3H2O(l) the rate of disappearance of IO3–(aq) at a particular time and concentration is 2.4 × 10 -3 mol/(L · s). What is the rate of appearance of I2(aq)? Answer –7.2 × 10-3 mol/(L · s) 2.4 × 10-3 mol/(L · s) 7.2 × 10-3 mol/(L · s) 8.0 × 10-3 mol/(L · s) 1.3 × 10-3 mol/(L · s) 6.7 points Question 3 1. The strongest intermolecular forces between molecules of PH3 are Answer ionic bonds. hydrogen bonds. dipole–dipole attractions. London forces. covalent bonds. 6.7 points Question 4 1. Which of the following equilibria would be affected by volume changes at constant temperature? Answer C2H4(g) + H2(g) C2H6(g) SO3(g) + NO(g) NO2(g) + SO2(g) 2HCl(g) 2HF(g) H2(g) + Cl2(g) H2(g) + F2(g) HCl(aq) + NaOH(aq) 6.7 points H2O(l) + NaCl(aq) Question 5 1. Which of the following is not a colligative property? Answer freezing-point lowering boiling-point elevation solute solubility osmotic pressure vapor-pressure lowering 6.7 points Question 6 1. For the elementary reaction A + B → C + D, what is the predicted rate law? Answer Rate = k[A][B] Rate = k[A]2 Rate = k[B]2 Rate = k Rate = k[A]/[C] 6.7 points Question 7 1. Consider the combustion of methane (as represented by the following equation). This is the reaction that occurs for a Bunsen burner, which is a source of heat for chemical reactions in the laboratory. CH4(g) + 2O2(g) CO2(g) + 2H2O(g) For the system at chemical equilibrium, which of the following explains what happens if the temperature is raised? Answer The equilibrium position is shifted to the right, and the value for K increases. The equilibrium position is shifted to the right, and the value for K decreases. The equilibrium position is shifted to the left, and the value for K decreases. The equilibrium position is shifted to the left, and the value for K increases. The equilibrium position is shifted, but the value for K stays constant. 6.7 points Question 8 1. The fact that the boiling point of a pure solvent is lower than the boiling point of a solution of the same solvent is a direct consequence of the Answer vapor pressure of the solution being higher than the vapor pressure of the pure solvent. vapor pressure of the solution being lower than the vapor pressure of the pure solvent. osmotic pressure of the solvent being higher than the osmotic pressure of the solution. osmotic pressure of the solvent being lower than the osmotic pressure of the solution. freezing-point depression of the solution. 6.7 points Question 9 1. Given the equilibrium constants for the following reactions: 4Cu(s) + O2(g) 2Cu2O(s); K1 4CuO(s) 2Cu2O(s) + O2(g); K2 What is K for the system 2Cu(s) + O2(g) equivalent to? 2CuO(s) Answer K1 × K2 {(K2)/(K1)}½ {(K1)/(K2)}½ (K2)½/(K1) (K1)(K2)½ 6.7 points Question 10 1. Consider the following equilibrium: O2(g) + 2F2(g) 2OF2(g); Kp = 2.3 × 10–15 Which of the following statements is true? Answer If the reaction mixture initially contains only OF2(g), then the total pressure at equilibrium will be less than the total initial pressure. If the reaction mixture initially contains only O2(g) and F2(g), then at equilibrium, the reaction mixture will consist of essentially only OF2(g). If the reaction mixture initially contains only O2(g) and F2(g), then the total pressure at equilibrium will be greater than the total initial pressure. If the reaction mixture initially contains only OF2(g), then at equilibrium, the reaction mixture will consist of essentially only O2(g) and F2(g). For this equilibrium, Kc = Kp. 6.7 points Question 11 1. Which of the following pure substances is a solid at room temperature and pressure? Answer NH3 PH3 AlH3 CH4 SiH4 6.7 points Question 12 1. A sulfuric acid solution that is 65.0% H2SO4 by mass has a density of 1.55 g/mL at 20°C. What is the molality of sulfuric acid in the solution? Answer 0.0243 m 41.1 m 1.01 m 0.650 m 18.9 m 6.7 points Question 13 1. A 3.140 molal solution of NaCl is prepared. How many grams of NaCl are present in a sample containing 2.901 kg of water? Answer 910.9 g 155.9 g 322.9 g 532.3 g none of these 6.7 points Question 14 1. In a first-order reaction, the half-life is 132 minutes. What is the rate constant? Answer 8.75 × 10-5 s-1 1.26 × 10-4 s-1 5490 s-1 0.315 s-1 5.25 × 10-3 s-1 6.7 points Question 15 1. In the reaction 2H2O2(aq) → 2H2O(l) + O2(g), the initial concentration of H2O2 is 0.519 M and, 26.2 s later, the concentration of H2O2 is 0.365 M. What is the initial rate of the reaction? Answer 0.00588 M/s –0.00294 M/s –0.00588 M/s 0.00294 M/s 0.0139 M/s 6.7 points Question 16 1. When cobalt chloride is added to pure water, the Co 2+ ions hydrate. The hydrated form then reacts with the Cl– ions to set up the equilibrium shown here: Co(H2O)62+ + 4Cl– (pink) CoCl42– + 6H2O (blue) Which statement describes the change that the system will undergo if silver nitrate is added? Answer It should become more blue. It should become more pink. Water will be produced. The silver ion will react with the CoCl42–. Nothing will change. 6.7 points Question 17 1. The following equilibrium is exothermic. How could the yield of diiodine pentoxide be increased? I2(g) + 5CO2(g) 5CO(g) + I2O5(g) Answer by increasing the pressure by decreasing the pressure by increasing the temperature by decreasing the temperature by decreasing the volume of the reaction vessel 6.7 points Question 18 1. The following data were obtained for the hypothetical reaction 2A + B → products. [A]0 (M) [B]0 (M) Initial Rate (M/s) 0.2 0.1 5 0.2 0.2 20 0.6 0.1 15 What is the overall order of this reaction? Answer 0 1/2 1 4 3 6.7 points Question 19 1. The phrase "the heat absorbed or released by a system undergoing a physical or chemical change at constant pressure" is Answer the definition of a state function. the change in enthalpy of the system. a statement of Hess's law. the change in internal energy of the system. the temperature change of the system. 6.7 points Question 20 1. A first-order chemical reaction is observed to have a rate constant of 32 min-1. What is the corresponding half-life for the reaction? Answer 46 min 1.3 min 45.8 s 1.3 s 1.9 s 6.7 points Question 21 1. For the equilibrium N2O4(g) 2NO2(g), at 298 K, Kp = 0.15. For this reaction system, it is found that the partial pressure of N2O4 is 3.5 10-2 atm at equilibrium. What is the partial pressure of NO2 at equilibrium? (R = 0.0821 L · atm/(K · mol)) Answer 0.0053 atm 23 atm 0.072 atm 0.0018 atm 4.8 atm 6.7 points Question 22 1. The metal iron crystallizes in a body-centered cubic lattice. If the density of iron is 7.87 g/cm3, what is the atomic volume of iron? Answer 8.02 × 106 pm3 1.44 × 105 pm3 4.01 × 106 pm3 1.59 × 105 pm3 7.96 × 104 pm3 6.7 points Question 23 1. For the endothermic reaction 2CO2(g) + N2(g) 2NO(g) + 2CO(g), the conditions that favor maximum conversion of the reactants to products are Answer high temperature and high pressure. high temperature, pressure being unimportant. high temperature and low pressure. low temperature and high pressure. low temperature and low pressure. 6.7 points Question 24 1. Two substances A and B react with each other in such a way that one-half of A remains after 25 min and one-fourth of A remains after 50 min. Doubling the concentration of B while keeping the concentration of A fixed doubles the rate of the reaction. This reaction is Answer zero-order in both A and B. first-order in both A and B. first-order in A and second-order in B. second-order in A and first-order in B. second-order in both A and B. 6.7 points Question 25 1. The formation reaction for NH3(g) is Answer N(g) + 3H(g) → NH3(g). N(g) + H2(g) → NH3(g). N2(g) + 3H(g) → NH3(g). N2(g) + H2(g) → NH3(g). N2(g) + H2(g) → NH3(g). 6.7 points Question 26 1. The molecules in a sample of solid SO2 are attracted to each other by a combination of Answer London forces and H-bonding. H-bonding and ionic bonding. covalent bonding and dipole-dipole interactions. London forces and dipole-dipole interactions. none of these 6.7 points Question 27 1. Below is a phase diagram for a substance. Which line represents the melting-point curve of the substance? Answer M-N R-X X-Z S-X S-Z 6.7 points Question 28 1. What is the mass percent of ethylene glycol (HOCH2CH2OH) in a solution of ethylene glycol in water that has a freezing point of –15.0°C? (Kf for water is 1.858°C/m.) Answer 33.4% 99.8% 8.07% 50.1% 76.9% 6.7 points Question 29 1. When 0.0400 mol of HCl(aq) is reacted with 0.0400 mol of NaOH(aq) in 50.0 mL of water, the temperature of the solution increases by 5.56°C. What is the enthalpy of reaction for the following thermochemical equation? HCl(aq) + NaOH(aq) → NaCl(aq) + H2O(l) Assume that the heat capacity of the solution and calorimeter is 401.5 J/°C. Answer –55.8 kJ –2.23 kJ 2.23 kJ 55.8 kJ –0.0893 kJ 6.7 points Question 30 1. Consider the following equilibrium: 4NH3(g) + 3O2(g) 2N2(g) + 6H2O(g) Suppose 0.30 mol of NH3 and 0.40 mol of oxygen are added to a 5.0-L container. If x mol of water is present at equilibrium, how many moles of ammonia will remain at equilibrium? Answer 0.30 – x 0.40 – x x 0.30 – x 0.30 – x