Multiple Choice 2 POINTS EACH Select the choice that best answers the question. Mark it clearly on your answer sheet.

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1 Chemistry Points Take Home Exam Name: Student ID: Form A Multiple Choice 2 POINTS EACH Select the choice that best answers the question. Mark it clearly on your answer sheet. 1. Likes dissolve likes is a reliable and time-tested rule-of-thumb that students should remember for the rest of their lives. Which choice best embodies what this expression means. (A) CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 in a polar solvent. should dissolve (B) CH 3 CH 2 CH 2 CH 2 CH 3 should not dissolve in gasoline or kerosine. (C) CH 3 CH 2 OH should dissolve in water. (D) CH 3 COOH should dissolve in a non-polar solvent like benzene or carbon tetrachloride. (E) MgSO 4 (s) should not dissolve in polar solvents. 2. Dipole-dipole (including H-bonding), ion-ion, and dispersion forces are the main types of intermolecular forces that dictate in large part the bulk properties of solids, liquids and gases. Rank the following intermolecular forces from strongest (left) to the weakest forces (right). (A) dipole-dipole > ion-ion > London dispersion (B) ion-ion > London dispersion > dipole-dipole (C) ion-ion > dipole-dipole > London dispersion (D) London dispersion > London dispersion > dipole-dipole (E) dipole-dipole > London dispersion > ion-ion 3. What is the strongest type of intermolecular force between acetone (CH 3 CCH 3 ) and methanol (CH 3 OH)? (A) ion-dipole forces (B) dipole-induced dipole forces (C) dispersion forces (D) hydrogen bonding (E) ion-ion force 4. Assuming ideal behavior, how many moles of solute particles are present in 3.00 ml of an aqueous, M AgNO3 solution? (A) (B) (C) (D) (E) How many grams of N 2 will dissolve in 2.0 L of water that is in contact with air at 25 C, where the partial pressure of N 2 is about 0.80 atm? (A) (B) (C) (D) (E) Which of the following statements is incorrect? (A) Polarizability is a measure of ease with which electron clouds are distorted in molecules or atoms. (B) The solubility of a solute in a solvent depends on temperature of the solvent. (C) The vapor pressure above a liquid does not vary with the temperature of the liquid. (D) The scattering of visible light (the Tyndall Effect) is a characteristic of colloidal solutions. 1

2 7. Which of the following statements is incorrect? (A) CH 3 CH 2 OH should have a viscosity and boiling point greater than HOCH 2 CH 2 CH 2 OH (B) The large specific heat capacity and the large heat of vaporization, H vap, of water are both a result of strong hydrogen-bonding forces. (C) The surface tension of a liquid is a result of strong and imbalanced intermolecular attractive forces acting at the surface of the liquid relative to its interior. (D) The observation that water forms a U-shaped meniscus climbing up the side of glassware is a result of cohesive forces being greater than adhesive forces. (E) Polar molecules is a result of moderate electronegativity differences between bonded atoms in molecules, but molecular geometry must be considered to determine if a molecule is polar overall. 8. Given the data of boiling points below, which of the following pure solvents will have the lowest vapor pressure and highest vapor pressure, respectively, at room temperature? Substance Boiling Point 1. ethanol, 78 C 2. methanol, 65 C 3. water, 100 C 4. acetone, 56 C 5. benzene, 80 C (A) 1 and 3, respectively (B) 1 and 4, respectively (C) 2 and 5, respectively (D) 3 and 4, respectively (E) 5 and 2, respectively 9. The first vertical line in the diagram below represents a thermometer showing the boiling point (bp) and freezing point (fp) for a pure solvent. Which line (1,2,3,4) best represents the boiling point and freezing of a solution relative to the values of for a pure solvent? (A) 1 (B) 2 (C) 3 (D) The colligative properties exhibited by dilute ideal solutions depends only on? (A) the strength of hydrogen bonds between the solute and the solvent. (B) the number of particles dissolved in a solution. (C) the identity and chemical properties of the solute dissolved in the solution. (D) the molecular weight of the solute molecules. (E) the polar and non-polar interactions between solute and solvent. 11. Which of the following best describes how to increase the solubility of a gas in a given solvent? (A) Decrease the partial pressure of the gas over the solvent (B) Increase the partial pressure of the gas over the solvent (C) Increase the temperature of the solvent (D) Decrease the temperature of the solvent (E) both A and B are correct (F) both A and C are correct (G) both B and C are correct (H) both B and D are correct 2

3 12. Choose the statement that is incorrect. (A) A 0.2m solution of Na 2 SO 4 (aq) would lower the freezing point of water more than a solution a 0.2m solution of NaCl(aq). (B) The solubility of gaseous-polar solutes like HCl(g), HF(g) or NH 3 (g) are less soluble in water than are non-polar gaseous solutes such as N 2 or O 2. (C) Solid substances that lack long-range order such as waxes, rubber, plastics and glass are amorphous solids. 16. A solution is prepared by dissolving 6.00 g of an unknown nonelectrolyte in enough water to make 1.00 L of solution. The osmotic pressure of this solution is atm at 25.0 C. What is the molecular weight of the unknown solute (R = Latm/Kmol)? (A) 110 g/mol (B) 196 g/mol (C) 5.1 g/mol (D) 179 g/mol (E) 16.4 g/mol 13. Which of the following aqueous solutions has the highest boiling point? K b for water is 0.52 C/m. (A) 0.2 m KCl (B) 0.2 m Na 2 SO 4 (C) 0.2 m Ca(NO 3 ) 2 (D) A and B. (E) B and C. 14. The vapor pressure of pure ethanol at 60 C is 349 torr. Raoult s law predicts what vapor pressure (in torr) at 60 C for a solution prepared by dissolving 10.0 mmol naphthalene (nonvolatile) in 90.0 mmol ethanol? (A) 349 torr 17. How many grams of ethylene glycol, HOCH 2 CH 2 OH, a common component of automobile antifreeze, must be added to g H 2 O to lower its freezing point to C? For water, K f = 1.86 C/m. (A) 2.69 g HOCH 2 CH 2 OH (B) 167 g HOCH 2 CH 2 OH (C) 16.7 g HOCH 2 CH 2 OH (D) g HOCH 2 CH 2 OH (E) 57.7 g (B) 336 torr (C) 314 torr (D) 34.9 torr (E) 38.8 torr 15. In how many grams of water should g of potassium nitrate (KNO 3 ) be dissolved to prepare a m solution? (A) g (B) 792 g (C) 1,000. g (D) 1,263 g (E) 7,917 g 18. The heat capacity of liquid water is 4.18 J/g C and the heat of vaporization is 40.7 kj/mol. How many kilojoules of heat must be provided to convert 1.00 g of liquid water at 67 C into 1.00 g of steam at 100 C? (A) 22.7 kj (B) 40.8 kj (C) 2.2 kj (D) 2,400 J (E) 40.8 J 3

4 19. During the process of osmosis (A) pure solvent diffuses through a membrane but solutes do not. (B) pure solutes diffuse through a membrane but solvent does not. (C) pure solvent and a solution both diffuse at the same time through a membrane. (D) gases diffuse through a membrane into a solution and build up pressure. 20. The solubility of CO 2 gas in water (A) increases with increasing temperature. (B) decreases with decreasing temperature and decreases with increasing pressure. (C) decreases with increasing temperature and increases with increasing pressure. (D) is not dependent on temperature or pressure. (E) CO 2 gas is not soluble in water. 21. A solution is prepared by dissolving 23.7 g of CaCl 2 in 375 g of water. The density of the resulting solution is 1.05 g/ml. Calculate the molarity of Cl in the solution described above. (A) M (B) M (C) 1.07 M (D) 1.12 M (E) M 22. A quantity of an inorganic salt is completely dissolved in a flask containing distilled water leaving the beaker cold to touch. What must be the signs of the following thermodynamic parameters for the dissolution of this ionic solid to have taken place? Choice H solution Temperature S solution For the reaction: BrO Br + 6 H + 3 Br H 2 O at a particular time, [Br ] = M/s. What is t [H + ] at the same instant? t (A) 7.8 M/s (B) M/s (C) M/s (D) M/s (E) 330M/s 24. Consider the following reaction: 2 D(g)+3 E(g)+ F(g) 2 G(g) + H(g) In one second, [G] increases by 0.20 mol/l. By how many mol/l does [E] decrease during the same time? (A) 0.30 (B) 0.60 (C) 0.20 (D) 0.45 (E) 0.13 (F) this question cannot be answered without knowing the rate law for this reaction. 25. Which three factors affect the rate of a chemical reaction? (A) temperature, reactant concentration, intermolecular forces between molecules (B) temperature, pressure, polarizability (C) catalyst, product concentration, and volume (D) temperature, product concentration, and container volume (E) temperature, reactant concentration, and presence of a catalyst 4

5 26. A catalyst accelerates a reaction because? (A) it increases the number of molecules with energy equal to or greater than the activation energy. (B) it increases the number of collisions between molecules (C) it lowers the activation energy for the reaction. (D) it increases the temperature of the molecules in the reaction. (E) it supplies energy to the reactant molecules. 27. What is the overall reaction order if the rate constant has units of L/(mol min)? (A) zero order (B) first order (C) second order (D) third order (E) none of the above 28. The reaction 2 NO 2 (g) 2 NO(g) + O 2 (g) is suspected to be second order in NO 2. Which of the following kinetic plots would be the most useful to confirm whether or not the reaction is second order? (A) a plot of [NO 2 ] 1 vs. t (B) a plot of ln [NO 2 ] vs. t (C) a plot of [NO 2 ] vs. t (D) a plot of ln [NO 2 ] 1 vs. t (E) a plot of [NO 2 ] 2 vs. t 29. For the overall chemical reaction shown below, which one of the following statements can be rightly assumed? 2H 2 S(g) + O 2 (g) 2S(s) + 2H 2 O(l) (A) The rate law can only be determined from experimental data (B) The reaction is third-order overall. (C) The reaction is second-order overall. (D) The rate law is, rate = k[h 2 S] 2 [O 2 ]. (E) The rate law is, rate = k[h 2 S] [O 2 ]. 30. Which statement is true about the half-life of a first-order reaction? (A) A larger rate constant corresponds to a longer half-life. (B) The half-life is directly proportional to the original concentration of the reactant. (C) The half-life is directly proportional to the final concentration of the reactant. (D) The half-life is inversely proportional to the rate constant. (E) The half-life is independent of temperature. 31. The reaction D products is first order, and the rate constant, k = s 1. If the initial concentration of D is 3.00 M, then what is the final concentration of D after 2.50 hr? (A) 0.26 M (B) 2.9 M (C) 34 M (D) 1.0 M (E) 0.57 M 32. For the chemical reaction A B + C, a plot of [A] t versus time is found to give a straight line with a negative slope. What is the order of reaction with respect to A? (A) zeroth (B) first (C) second (D) third (E) Such a plot cannot reveal the order of the reaction. 33. When the reaction aa cc + dd is studied, a plot of 1/[A] t vs. time gives a straight line with a positive slope. What is the order of the reaction? (A) third order (B) second order (C) first order (D) zero order (E) more information is needed to determine the order 5

6 34. A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives? (Note: we are asking for the fraction consumed, not the fraction remaining.) (A) (B) 0.13 (C) 0.25 (D) 0.50 (E) Consider the reaction A + B C. If it is determined experimentally that the reaction rate doubles when the concentration of A doubles, and that when the concentrations of A and B are both doubled, the rate increases by a factor of 8. What must be the rate law for this reaction? (A) rate = k[a][b] 2 (B) rate = k[a][b] 3 (C) rate = k[a] 2 [B] 2 (D) rate = k[a] 2 [B] (E) rate = k[a][b] 36. The reaction A + 2B products has been found to have the rate law, rate = k[a] 3 [B]. While holding the concentration of B constant, the concentration of A is increased from x to 3x. By what factor does the rate of reaction change? (A) 3 (B) 6 (C) 8 (D) 27 (E) the reaction rate does not change in this case 37. Many drugs are broken down in the body by a first-order process. The half-life of a particular drug is 5.00 hours. If a patient takes a 100. mg dose, how many mg remain in the bloodstream after 12.0 hours? (A) 0 (B) 1.66 (C) 5.28 (D) 15.2 (E) The activation energy of a reaction is 50.0 kj/mol, and the rate constant is at room temperature (300 K). What is the rate constant at 330 K? (A) 1.82 (B) (C) (D) (E) The decomposition of dinitrogen pentaoxide has an activation energy of 102 kj/mol and H rxn = +55 kj/mol. What is the activation energy for the reverse reaction? (A) 27 kj/mol (B) 47 kj/mol (C) 55 kj/mol (D) 102 kj/mol (E) 157 kj/mol (F) More information is needed, since this is a Hess s law calculation. Section 2. (Long Answer 13.3 pts each) Answer the following three questions. Show all your work in an organized and neat fashion in your blue book to receive partial credit. 40. Use the phase diagram of a substance shown below to answer everything that is asked in the following questions. 6

7 (A) What is line A-B in the diagram, and the areas just below and above this line? solid-liquid line (B) What is point B and its signficance? (C) Which numbered dashed line (1-6 representing temperature) corresponds to the normal boiling point temperature of this substance? (D) Which numbered dashed line (1-6 representing temperature) corresponds to the normal freezing point temperature of this substance? (E) How does the density of the solid phase compare with the density of the liquid phase in this substance? (F)Starting at Point C and traversing to Point D on the diagram, indicate the phase and what occurs. (G) What is Point E on the diagram and its significance? 7

8 Multiple Choice 2 POINTS EACH Answer Key for Exam A Select the choice that best answers the question. Mark it clearly on your answer sheet. 1. Likes dissolve likes is a reliable and time-tested rule-of-thumb that students should remember for the rest of their lives. Which choice best embodies what this expression means. (A) CH 3 CH 2 CH 2 CH 2 CH 2 CH 3 should dissolve in a polar solvent. (B) CH 3 CH 2 CH 2 CH 2 CH 3 should not dissolve in gasoline or kerosine. (C) CH 3 CH 2 OH should dissolve in water. (D) CH 3 COOH should dissolve in a non-polar solvent like benzene or carbon tetrachloride. (E) MgSO 4 (s) should not dissolve in polar solvents. 2. Dipole-dipole (including H-bonding), ion-ion, and dispersion forces are the main types of intermolecular forces that dictate in large part the bulk properties of solids, liquids and gases. Rank the following intermolecular forces from strongest (left) to the weakest forces (right). (A) dipole-dipole > ion-ion > London dispersion (B) ion-ion > London dispersion > dipole-dipole (C) ion-ion > dipole-dipole > London dispersion (D) London dispersion > London dispersion > dipole-dipole (E) dipole-dipole > London dispersion > ion-ion 3. What is the strongest type of intermolecular force between acetone (CH 3 CCH 3 ) and methanol (CH 3 OH)? (A) ion-dipole forces (B) dipole-induced dipole forces (C) dispersion forces (D) hydrogen bonding (E) ion-ion force 4. Assuming ideal behavior, how many moles of solute particles are present in 3.00 ml of an aqueous, M AgNO3 solution? (A) (B) (C) (D) (E)

9 5. How many grams of N 2 will dissolve in 2.0 L of water that is in contact with air at 25 C, where the partial pressure of N 2 is about 0.80 atm? (A) (B) (C) (D) (E) Which of the following statements is incorrect? (A) Polarizability is a measure of ease with which electron clouds are distorted in molecules or atoms. (B) The solubility of a solute in a solvent depends on temperature of the solvent. (C) The vapor pressure above a liquid does not vary with the temperature of the liquid. (D) The scattering of visible light (the Tyndall Effect) is a characteristic of colloidal solutions. 7. Which of the following statements is incorrect? (A) CH 3 CH 2 OH should have a viscosity and boiling point greater than HOCH 2 CH 2 CH 2 OH (B) The large specific heat capacity and the large heat of vaporization, H vap, of water are both a result of strong hydrogen-bonding forces. (C) The surface tension of a liquid is a result of strong and imbalanced intermolecular attractive forces acting at the surface of the liquid relative to its interior. (D) The observation that water forms a U-shaped meniscus climbing up the side of glassware is a result of cohesive forces being greater than adhesive forces. (E) Polar molecules is a result of moderate electronegativity differences between bonded atoms in molecules, but molecular geometry must be considered to determine if a molecule is polar overall. 8. Given the data of boiling points below, which of the following pure solvents will have the lowest vapor pressure and highest vapor pressure, respectively, at room temperature? Substance Boiling Point 1. ethanol, 78 C 2. methanol, 65 C 3. water, 100 C 4. acetone, 56 C 5. benzene, 80 C (A) 1 and 3, respectively (B) 1 and 4, respectively (C) 2 and 5, respectively (D) 3 and 4, respectively (E) 5 and 2, respectively 2

10 9. The first vertical line in the diagram below represents a thermometer showing the boiling point (bp) and freezing point (fp) for a pure solvent. Which line (1,2,3,4) best represents the boiling point and freezing of a solution relative to the values of for a pure solvent? (A) 1 (B) 2 (C) 3 (D) The colligative properties exhibited by dilute ideal solutions depends only on? (A) the strength of hydrogen bonds between the solute and the solvent. (B) the number of particles dissolved in a solution. (C) the identity and chemical properties of the solute dissolved in the solution. (D) the molecular weight of the solute molecules. (E) the polar and non-polar interactions between solute and solvent. 11. Which of the following best describes how to increase the solubility of a gas in a given solvent? (A) Decrease the partial pressure of the gas over the solvent (B) Increase the partial pressure of the gas over the solvent (C) Increase the temperature of the solvent (D) Decrease the temperature of the solvent (E) both A and B are correct (F) both A and C are correct (G) both B and C are correct (H) both B and D are correct 12. Choose the statement that is incorrect. (A) A 0.2m solution of Na 2 SO 4 (aq) would lower the freezing point of water more than a solution a 0.2m solution of NaCl(aq). (B) The solubility of gaseous-polar solutes like HCl(g), HF(g) or NH 3 (g) are less soluble in water than are non-polar gaseous solutes such as N 2 or O 2. (C) Solid substances that lack long-range order such as waxes, rubber, plastics and glass are amorphous solids. 13. Which of the following aqueous solutions has the highest boiling point? K b for water is 0.52 C/m. (A) 0.2 m KCl (B) 0.2 m Na 2 SO 4 (C) 0.2 m Ca(NO 3 ) 2 (D) A and B. (E) B and C. 3

11 14. The vapor pressure of pure ethanol at 60 C is 349 torr. Raoult s law predicts what vapor pressure (in torr) at 60 C for a solution prepared by dissolving 10.0 mmol naphthalene (nonvolatile) in 90.0 mmol ethanol? (A) 349 torr (B) 336 torr (C) 314 torr (D) 34.9 torr (E) 38.8 torr 15. In how many grams of water should g of potassium nitrate (KNO 3 ) be dissolved to prepare a m solution? (A) g (B) 792 g (C) 1,000. g (D) 1,263 g (E) 7,917 g 16. A solution is prepared by dissolving 6.00 g of an unknown nonelectrolyte in enough water to make 1.00 L of solution. The osmotic pressure of this solution is atm at 25.0 C. What is the molecular weight of the unknown solute (R = Latm/Kmol)? (A) 110 g/mol (B) 196 g/mol (C) 5.1 g/mol (D) 179 g/mol (E) 16.4 g/mol 17. How many grams of ethylene glycol, HOCH 2 CH 2 OH, a common component of automobile antifreeze, must be added to g H 2 O to lower its freezing point to C? For water, K f = 1.86 C/m. (A) 2.69 g HOCH 2 CH 2 OH (B) 167 g HOCH 2 CH 2 OH (C) 16.7 g HOCH 2 CH 2 OH (D) g HOCH 2 CH 2 OH (E) 57.7 g 18. The heat capacity of liquid water is 4.18 J/g C and the heat of vaporization is 40.7 kj/mol. How many kilojoules of heat must be provided to convert 1.00 g of liquid water at 67 C into 1.00 g of steam at 100 C? (A) 22.7 kj (B) 40.8 kj (C) 2.2 kj (D) 2,400 J (E) 40.8 J 4

12 19. During the process of osmosis (A) pure solvent diffuses through a membrane but solutes do not. (B) pure solutes diffuse through a membrane but solvent does not. (C) pure solvent and a solution both diffuse at the same time through a membrane. (D) gases diffuse through a membrane into a solution and build up pressure. 20. The solubility of CO 2 gas in water (A) increases with increasing temperature. (B) decreases with decreasing temperature and decreases with increasing pressure. (C) decreases with increasing temperature and increases with increasing pressure. (D) is not dependent on temperature or pressure. (E) CO 2 gas is not soluble in water. 21. A solution is prepared by dissolving 23.7 g of CaCl 2 in 375 g of water. The density of the resulting solution is 1.05 g/ml. Calculate the molarity of Cl in the solution described above. (A) M (B) M (C) 1.07 M (D) 1.12 M (E) M 22. A quantity of an inorganic salt is completely dissolved in a flask containing distilled water leaving the beaker cold to touch. What must be the signs of the following thermodynamic parameters for the dissolution of this ionic solid to have taken place? Choice H solution Temperature S solution For the reaction: BrO Br + 6 H + 3 Br H 2 O at a particular time, [Br ] t What is [H+ ] at the same instant? t = M/s. (A) 7.8 M/s (B) M/s (C) M/s (D) M/s (E) 330M/s 5

13 24. Consider the following reaction: 2 D(g) + 3 E(g) + F(g) 2 G(g) + H(g) In one second, [G] increases by 0.20 mol/l. By how many mol/l does [E] decrease during the same time? (A) 0.30 (B) 0.60 (C) 0.20 (D) 0.45 (E) 0.13 (F) this question cannot be answered without knowing the rate law for this reaction. 25. Which three factors affect the rate of a chemical reaction? (A) temperature, reactant concentration, intermolecular forces between molecules (B) temperature, pressure, polarizability (C) catalyst, product concentration, and volume (D) temperature, product concentration, and container volume (E) temperature, reactant concentration, and presence of a catalyst 26. A catalyst accelerates a reaction because? (A) it increases the number of molecules with energy equal to or greater than the activation energy. (B) it increases the number of collisions between molecules (C) it lowers the activation energy for the reaction. (D) it increases the temperature of the molecules in the reaction. (E) it supplies energy to the reactant molecules. 27. What is the overall reaction order if the rate constant has units of L/(mol min)? (A) zero order (B) first order (C) second order (D) third order (E) none of the above 28. The reaction 2 NO 2 (g) 2 NO(g) + O 2 (g) is suspected to be second order in NO 2. Which of the following kinetic plots would be the most useful to confirm whether or not the reaction is second order? (A) a plot of [NO 2 ] 1 vs. t (B) a plot of ln [NO 2 ] vs. t (C) a plot of [NO 2 ] vs. t (D) a plot of ln [NO 2 ] 1 vs. t (E) a plot of [NO 2 ] 2 vs. t 6

14 29. For the overall chemical reaction shown below, which one of the following statements can be rightly assumed? 2H 2 S(g) + O 2 (g) 2S(s) + 2H 2 O(l) (A) The rate law can only be determined from experimental data (B) The reaction is third-order overall. (C) The reaction is second-order overall. (D) The rate law is, rate = k[h 2 S] 2 [O 2 ]. (E) The rate law is, rate = k[h 2 S] [O 2 ]. 30. Which statement is true about the half-life of a first-order reaction? (A) A larger rate constant corresponds to a longer half-life. (B) The half-life is directly proportional to the original concentration of the reactant. (C) The half-life is directly proportional to the final concentration of the reactant. (D) The half-life is inversely proportional to the rate constant. (E) The half-life is independent of temperature. 31. The reaction D products is first order, and the rate constant, k = s 1. If the initial concentration of D is 3.00 M, then what is the final concentration of D after 2.50 hr? (A) 0.26 M (B) 2.9 M (C) 34 M (D) 1.0 M (E) 0.57 M 32. For the chemical reaction A B + C, a plot of [A] t versus time is found to give a straight line with a negative slope. What is the order of reaction with respect to A? (A) zeroth (B) first (C) second (D) third (E) Such a plot cannot reveal the order of the reaction. 33. When the reaction aa cc + dd is studied, a plot of 1/[A] t vs. time gives a straight line with a positive slope. What is the order of the reaction? (A) third order (B) second order (C) first order (D) zero order (E) more information is needed to determine the order 7

15 34. A reactant R is being consumed in a first-order reaction. What fraction of the initial R is consumed in 4.0 half-lives? (Note: we are asking for the fraction consumed, not the fraction remaining.) (A) (B) 0.13 (C) 0.25 (D) 0.50 (E) Consider the reaction A + B C. If it is determined experimentally that the reaction rate doubles when the concentration of A doubles, and that when the concentrations of A and B are both doubled, the rate increases by a factor of 8. What must be the rate law for this reaction? (A) rate = k[a][b] 2 (B) rate = k[a][b] 3 (C) rate = k[a] 2 [B] 2 (D) rate = k[a] 2 [B] (E) rate = k[a][b] 36. The reaction A + 2B products has been found to have the rate law, rate = k[a] 3 [B]. While holding the concentration of B constant, the concentration of A is increased from x to 3x. By what factor does the rate of reaction change? (A) 3 (B) 6 (C) 8 (D) 27 (E) the reaction rate does not change in this case 37. Many drugs are broken down in the body by a first-order process. The half-life of a particular drug is 5.00 hours. If a patient takes a 100. mg dose, how many mg remain in the bloodstream after 12.0 hours? (A) 0 (B) 1.66 (C) 5.28 (D) 15.2 (E) The activation energy of a reaction is 50.0 kj/mol, and the rate constant is at room temperature (300 K). What is the rate constant at 330 K? (A) 1.82 (B) (C) (D) (E)

16 39. The decomposition of dinitrogen pentaoxide has an activation energy of 102 kj/mol and H rxn = +55 kj/mol. What is the activation energy for the reverse reaction? (A) 27 kj/mol (B) 47 kj/mol (C) 55 kj/mol (D) 102 kj/mol (E) 157 kj/mol (F) More information is needed, since this is a Hess s law calculation. Section 2. (Long Answer 13.3 pts each) Answer the following three questions. Show all your work in an organized and neat fashion in your blue book to receive partial credit. 40. Use the phase diagram of a substance shown below to answer everything that is asked in the following questions. (A) What is line A-B in the diagram, and the areas just below and above this line? solid-liquid line (B) What is point B and its signficance? (C) Which numbered dashed line (1-6 representing temperature) corresponds to the normal boiling point temperature of this substance? (D) Which numbered dashed line (1-6 representing temperature) corresponds to the normal freezing point temperature of this substance? (E) How does the density of the solid phase compare with the density of the liquid phase in this substance? (F)Starting at Point C and traversing to Point D on the diagram, indicate the phase and what occurs. (G) What is Point E on the diagram and its significance? A) solid-gas line, or sublimation-deposition (equilibrium) line, or solid-gas (equilbrium) points 1pt Above line=solid phase or P,T points where the substance is solid; 0.5pt Below line gas phase or P,T points where the substance is a gas: 0.5pt (B) B is the Triple point 1pt Significance: P,T where all phases of a substance are in equilibrium (or all possible phase transitions occurring/equilibrium at the same time: 1 pt 9

17 (C) Which dashed line (1-6) corresponds to the normal boiling point of this substance? Line 5 (D) Which dashed line (1-6) corresponds to the normal freezing point of this substance? Line 3 2pt 2pt (E) How does the density of this substance solid phase compare with the density of its liquid phase (the same, higher, lower, indeterminate)? Solid is of higher density 1 pt (F) Point C Gas (1pt) and Point D is liquid (1pt) respectively 2 pt (G) What is Point E on the diagram and its significance (explain with reference to the pressure and temperature at Point E) (2.3pts)? Point E is called the critical point 1.3pt Significance: P,T point beyond which liquid and gas phases are indistinguishable and called a supercritical fluid. P is called critical pressure, T c is critical temperature. Beyond T c no applied pressure can condense the gas to a liquid. 1 pt 10