CHE 107 Spring 2018 Exam 2

Transcription

1 CHE 107 Spring 2018 Exam 2 Your Name: Your ID: Question #: 1 Which substance has the smallest standard molar entropy ( S)? A He(g) B H2O(g) C CH4(g) D F2(g) Question #: 2 Phosgene, a chemical weapon used during World War I, is formed by the reaction of chloroform with oxygen: 2 CHCl3(l) + O2(g) 2 COCl2(g) + 2 HCl(g) ΔHº = 353 kj The sign of the entropy change for the system, ΔSsys, is 1 [positive, negative] The sign of the entropy change for the surroundings, ΔSsurr, is 2 [positive, negative] The sign of the entropy change for the universe, ΔSuniv, is 3 [positive, negative] The reaction will be 4 [spontaneous, nonspontaneous]

2 Question #: 3 For this reaction at 298 K and constant pressure, ΔSsurroundings = 3 CO2(g) + 4 H2O(g) C3H8(g) + 5 O2(g) ΔH = 2043 kj A ΔSsurroundings = 729 J/K B ΔSsurroundings = 729 J/K C ΔSsurroundings = 6,860 J/K D ΔSsurroundings = 6,860 J/K Question #: 4 Given the information below, what is ΔS rxn for 2 C4H10(l) + 13 O2(g) 8 CO2(g) + 10 H2O(l) Compound S (J/mol K) C4H10(l)) 310 O2(g) 205 CO2(g) 214 H2O(l) 700 A 799 J/mol K B 873 J/mol K C 363 kj/mol K D 799 J/mol K Question #: 5 Given NaHCO3(s) + HCl(aq) NaCl(aq) + H2O(l) + CO2(g); ΔH = 285 kj mol 1 ; ΔS = 230 J mol 1 K 1 above what Kelvin temperature will this reaction become spontaneous? A 24 K B 85 K C 106 K D 124 K

3 Question #: 6 Calculate the free energy change, ΔGºrxn, for this reaction at 250 C 2 Ca(s) + O2(g) 2 CaO(s); ΔHºrxn = 1270 kj; ΔSºrxn = 365 J/K A kj B kj C kj D kj Question #: 7 What is ΔG rxn for the reaction 3 C(s) + 4 H2(g) C3H8(g) given the information below? ΔG rxn (kj) Reaction A: 3 CO2(g) + 4 H2O(g) C3H8(g) + 5 O2(g) 2074 Reaction B: CO2(g) C(s) + O2(g) 394 Reaction C: 2 H2(g) + O2(g) 2 H2O(g) 457 A 22 kj B 2625 kj C 1805 kj D 52 kj

4 Question #: 8 Which two statements about ΔHsolution are true? ΔHsolution = ΔHmix + ΔHsolute + ΔHsolvent A ΔHsolution will be endothermic when ΔHsolute + ΔHsolvent >ΔHmix B ΔHsolution will always be exothermic when ΔHsolute + ΔHsolvent = ΔHmix C ΔHsolution will be exothermic when the solute-solvent intermolecular forces are stronger than the sum of the solute-solute and solvent-solvent intermolecular forces D Solutions only form when ΔHsolution is exothermic Question #: 9 Using the solubility curves shown below, describe the solubility of the following salts in 1000 g of water, each at 200 ºC Respond with saturated, unsaturated, or supersaturated grams of KCl grams of KNO3 1 2

5 Question #: 10 An aqueous solution is saturated in both CO2(g) and KCl(aq) at 25 ºC If the solution is cooled to 0 C, which process is most likely to occur? A Some CO2 vaporizes but no KCl precipitates B No CO2 vaporizes but some KCl precipitates C Some CO2 vaporizes and some KCl precipitates D All the CO2 vaporizes and all the KCl precipitates Question #: 11 What is the concentration of NH3 when the partial pressure of ammonia, PNH3, is 025 atm above the solution at 25 C? An 87 M NH3 solution results when the pressure of PNH3 is 015 atm at 25 C? A 76 M B 12 M C 18 M D 15 M Question #: 12 The vapor pressure of pure benzene, C6H6 (781 g/mol), is 400 mmhg at 601 ºC What is the vapor pressure at 601 ºC of a solution prepared by dissolving 492 g of camphor, C10H16O (1522 g/mol), in 197 g of benzene? Camphor is a nonvolatile, nonionizing solute 1 mmhg Report your answer with three significant figures Do NOT include units in your answer 1

6 Question #: 13 What is the boiling point of a solution of 106 g potassium phosphate (K3PO4, 212 g/mol) in g H2O? Kb(H2O) = 0512 ºC/m and Tb = 1000 C for the boiling point of pure water Use ideal van't Hoff factors, if needed A 102 C B 104 C C 106 C D 108 C Question #: 14 An osmotic cell with a semipermeable membrane is set up with pure water in chamber A and 150 M KCl in chamber B What happens as the cell reaches equilibrium? A The volumes in chamber A and chamber B remain equal B H2O from chamber A flows into chamber B, increasing the volume in chamber B C KCl from chamber B flows into chamber A, increasing the volume in chamber A D H2O from chamber B flows into chamber A, increasing the volume in chamber A

7 Question #: 15 The ideal van't Hoff factor for (NH4)3PO4 is 1 Report your answer as a whole number Do NOT include units in your answer 1 Question #: 16 Assuming an ideal van't Hoff factor, what mass of NaCl (584 g/mol) needs to be added to 100 kg of water to lower the freezing point of water by 300 ºC? Kf for water is 186 ºC/m 1 g NaCl Report your answer with three significant figures Do NOT include units with your answer 1 Question #: 17 A 600 g sample of an unknown nonelectrolyte is dissolved in 240 g of carbon tetrachloride, CCl4, to make a solution that boils at 8535 C The Kb value for CCl4 is 503 C/m and the boiling point of pure CCl4 is 7680 C What is the molar mass of the unknown compound? A 407 g/mol B 118 g/mol C 122 g/mol D 147 g/mol Question #: 18 NO2(g) reacts with water to form nitric acid, HNO3 3 NO2(g) + H2O(l) 2 HNO3(aq) + NO(g) What is the rate at which HNO3 is being formed when NO2 is reacting at 090 M/s? Report your answer with two significant figures Do NOT include units with your answer 1 M/s 1

8 Question #: 19 Given the following reaction and data, what is the rate law for the reaction? I (aq) + OCl (aq) Cl (aq) + OI (aq) [I ] (M) [OCl ] (M) Initial Rate (M/s) A rate = k[i ][OCl ] 2 B rate = k[i ][OCl ] C rate = k[i ] 2 [OCl ] D rate = k[ocl ] 2 Question #: 20 The gas phase reaction NO2(g) + CO(g) NO(g) + CO2(g) is found to be second-order in NO2 and zero-order in CO at temperatures less than 500 K What is the effect on the rate if the concentration of NO2 is tripled and the concentration of CO is doubled? A The rate increases by a factor of 6 B The rate increases by a factor of 18 C The rate increases by a factor of 9 D The rate increases by a factor of 3

9 Question #: 21 For the reaction A B, fill in the blanks with zero, first, or second for the kinetic data graphed below A reaction is 1 -order when a plot of ln [A] versus time is linear A reaction is 2 -order when the plot of 1/[A] versus time is linear A reaction is 3 -order when a plot of [A] versus time is linear Question #: 22 Using the given data, determine the rate constant, k, of the reaction 2 ClO2(aq) + 2 OH (aq) ClO3 (aq) + ClO2 (aq) + H2O(l) where rate = k[oh ] Trial [ClO2] (M) [OH ] (M) Rate (M/s) A s 1 B 14 s 1 C s 1 D 083 s 1

10 Question #: 23 Radioactive technetium-99 (Tc-99) decays following first order kinetics with k = 0116 h 1 How much Tc-99 remains after 22 hours in a solution initially 0500 M in Tc-99? A 0187 M B 0297 M C 0387 M D 0407 M Question #: 24 The decomposition below is second order in NO2 How long will it take for the concentration of NO2 to decrease from 400 M to 100 M? NO2(g) NO(g) + ½ O2(g) k = 34 M 1 min 1 A 088 min B 14 min C 022 min D 0074 min Question #: 25 When heated to 499 C, cyclopropane rearranges (isomerizes) and forms propene with a rate constant of min 1 What is the half-life of this reaction, in minutes? Report your answer to three significant figures Do NOT include units in your answer 1 minutes 1

11 Question #: 26 The activation energy for a certain reaction is 255 kj and the ΔHrxn is 121 kj What is the activation energy of the reverse reaction? A 255 kj B 376 kj C 134 kj D 121 kj Question #: 27 A certain reaction has an activation energy of 254 kj/mol At what temperature will the reaction will proceed four times faster than it does at 298 K? A 294 K B 739 K C 302 K D 1190 K Question #: 28 In the diagram below, the 1 of the reaction is greater than the 2 needed to reach the 3 before proceeding to products Fill in the blanks with activation energy, enthalpy, or transition state 1 2 3

12 Question #: 29 Which two statements about catalysts are false? A A catalyst is a substance that lowers the activation energy of a chemical reaction B A catalyst is always an enzyme C A catalyst speeds up the rate of a reaction D A catalyst is consumed during the chemical reaction Question #: 30 The overall reaction 2O3(g) 3O2(g) can occur by the following mechanism: NO(g) + O 3 (g) NO2(g) + O2(g) O 3 (g) O 2 (g) + O(g) NO 2 (g) + O(g) NO(g) + O 2 (g) Select the TWO intermediates in this mechanism NO(g) + O 3(g) NO2(g) + O2(g) A NO(g) B O3(g) C NO2(g) D O2(g) E O(g)

13 DRAFT Do Not Use Until Posted CHE 107 Spring 2018 Exam 2 - Confidential Your Name: Your ID: attachment_for_pubexamuid_lnxp xx_255jpg Question #: 1 Which substance has the smallest standard molar entropy ( S)? A He(g) B H 2 O(g) C CH 4 (g) D F 2 (g) Question #: 2 Phosgene, a chemical weapon used during World War I, is formed by the reaction of chloroform with oxygen:

14 2 CHCl 3 (l) + O 2 (g) 2 COCl 2 (g) + 2 HCl(g) ΔHº = 353 kj The sign of the entropy change for the system, ΔS sys, is 1 [positive, negative] The sign of the entropy change for the surroundings, ΔS surr, is 2 [positive, negative] The sign of the entropy change for the universe, ΔS univ, is 3 [positive, negative] The reaction will be 4 [spontaneous, nonspontaneous] 1 positive + 2 positive + 3 positive + 4 spontaneous Question #: 3 For this reaction at 298 K and constant pressure, ΔS surroundings = 3 CO 2 (g) + 4 H 2 O(g) C 3 H 8 (g) + 5 O 2 (g) ΔH = 2043 kj A ΔS surroundings = 729 J/K B ΔS surroundings = 729 J/K C ΔS surroundings = 6,860 J/K D ΔS surroundings = 6,860 J/K Question #: 4 Given the information below, what is ΔS rxn for 2 C 4 H 10 (l) + 13 O 2 (g) 8 CO 2 (g) + 10 H 2 O(l) Compound S (J/mol K) C 4 H 10 (l)) 310 O 2 (g) 205 CO 2 (g) 214 H 2 O(l) 700

15 A 799 J/mol K B 873 J/mol K C 363 kj/mol K D 799 J/mol K Question #: 5 Given NaHCO 3 (s) + HCl(aq) NaCl(aq) + H 2 O(l) + CO 2 (g); ΔH = 285 kj mol 1 ; ΔS = 230 J mol 1 K 1 above what Kelvin temperature will this reaction become spontaneous? A 24 K B 85 K C 106 K D 124 K Question #: 6 Calculate the free energy change, ΔGº rxn, for this reaction at 250 C 2 Ca(s) + O 2 (g) 2 CaO(s); ΔHº rxn = 1270 kj; ΔSº rxn = 365 J/K A kj B kj C kj D kj Question #: 7 What is ΔG rxn for the reaction 3 C(s) + 4 H 2 (g) C 3 H 8 (g) given the information below? G rxn (kj) Reaction A: 3 CO 2 (g) + 4 H 2 O(g) C 3 H 8 (g) + 5 O 2 (g) 2074

16 Reaction B: CO 2 (g) C(s) + O 2 (g) 394 Reaction C: 2 H 2 (g) + O 2 (g) 2 H 2 O(g) 457 A 22 kj B 2625 kj C 1805 kj D 52 kj Question #: 8 Which two statements about ΔH solution are true? ΔH solution = ΔH mix + ΔH solute + ΔH solvent A ΔH solution will be endothermic when ΔH solute + ΔH solvent >ΔH mix B ΔH solution will always be exothermic when ΔH solute + ΔH solvent = ΔH mix C ΔH solution will be exothermic when the solute-solvent intermolecular forces are stronger than the sum of the solute-solute and solvent-solvent intermolecular forces D Solutions only form when ΔH solution is exothermic Question #: 9 Using the solubility curves shown below, describe the solubility of the following salts in 1000 g of water, each at 200 ºC Respond with saturated, unsaturated, or supersaturated grams of KCl grams of KNO 3

17 1 unsaturated 2 saturated Question #: 10 An aqueous solution is saturated in both CO 2 (g) and KCl(aq) at 25 ºC If the solution is cooled to 0 C, which process is most likely to occur? A Some CO 2 vaporizes but no KCl precipitates B No CO 2 vaporizes but some KCl precipitates C Some CO 2 vaporizes and some KCl precipitates D All the CO 2 vaporizes and all the KCl precipitates Question #: 11 What is the concentration of NH 3 when the partial pressure of ammonia, P NH3, is 025 atm above the solution at 25 C? An 87 M NH 3 solution results when the pressure of P NH3 is 015

18 atm at 25 C? A 76 M B 12 M C 18 M D 15 M Question #: 12 The vapor pressure of pure benzene, C 6 H 6 (781 g/mol), is 400 mmhg at 601 ºC What is the vapor pressure at 601 ºC of a solution prepared by dissolving 492 g of camphor, C 10 H 16 O (1522 g/mol), in 197 g of benzene? Camphor is a nonvolatile, nonionizing solute 1 mmhg Report your answer with three significant figures Do NOT include units in your answer Question #: 13 What is the boiling point of a solution of 106 g potassium phosphate (K 3 PO 4, 212 g/mol) in g H 2 O? K b (H 2 O) = 0512 ºC/m and T b = 1000 C for the boiling point of pure water Use ideal van't Hoff factors, if needed A 102 C B 104 C C 106 C D 108 C Question #: 14 An osmotic cell with a semipermeable membrane is set up with pure water in chamber A and 150 M KCl in chamber B What happens as the cell reaches equilibrium?

19 A The volumes in chamber A and chamber B remain equal B H 2 O from chamber A flows into chamber B, increasing the volume in chamber B C KCl from chamber B flows into chamber A, increasing the volume in chamber A D H 2 O from chamber B flows into chamber A, increasing the volume in chamber A Question #: 15 The ideal van't Hoff factor for (NH 4 ) 3 PO 4 is 1 Report your answer as a whole number Do NOT include units in your answer 1 4 four Question #: 16

20 Assuming an ideal van't Hoff factor, what mass of NaCl (584 g/mol) needs to be added to 100 kg of water to lower the freezing point of water by 300 ºC? K f for water is 186 ºC/m 1 g NaCl Report your answer with three significant figures Do NOT include units with your answer Question #: 17 A 600 g sample of an unknown nonelectrolyte is dissolved in 240 g of carbon tetrachloride, CCl 4, to make a solution that boils at 8535 C The K b value for CCl 4 is 503 C/m and the boiling point of pure CCl 4 is 7680 C What is the molar mass of the unknown compound? A 407 g/mol B 118 g/mol C 122 g/mol D 147 g/mol Question #: 18 NO 2 (g) reacts with water to form nitric acid, HNO 3 3 NO 2 (g) + H 2 O(l) 2 HNO 3 (aq) + NO(g) What is the rate at which HNO 3 is being formed when NO 2 is reacting at 090 M/s? Report your answer with two significant figures Do NOT include units with your answer 1 M/s Question #: 19 Given the following reaction and data, what is the rate law for the reaction? I (aq) + OCl (aq) Cl (aq) + OI (aq)

21 [I ] (M) [OCl Initial Rate ] (M) (M/s) A rate = k[i ][OCl ] 2 B rate = k[i ][OCl ] C rate = k[i ] 2 [OCl ] D rate = k[ocl ] 2 Question #: 20 The gas phase reaction NO 2 (g) + CO(g) NO(g) + CO 2 (g) is found to be second-order in NO 2 and zero-order in CO at temperatures less than 500 K What is the effect on the rate if the concentration of NO 2 is tripled and the concentration of CO is doubled? A The rate increases by a factor of 6 B The rate increases by a factor of 18 C The rate increases by a factor of 9 D The rate increases by a factor of 3 Question #: 21 For the reaction A B, fill in the blanks with zero, first, or second for the kinetic data graphed below

22 A reaction is 1 -order when a plot of ln [A] versus time is linear A reaction is 2 -order when the plot of 1/[A] versus time is linear A reaction is 3 -order when a plot of [A] versus time is linear 1 first 1st 2 second 2nd 3 zero 0 Question #: 22 Using the given data, determine the rate constant, k, of the reaction 2 ClO2(aq) + 2 OH (aq) ClO3 (aq) + ClO2 (aq) + H2O(l) where rate = k[oh ] Trial [ClO ] (M) 2 [OH ] (M) Rate (M/s) A s 1 B 14 s 1 C s 1 D 083 s 1

23 Question #: 23 Radioactive technetium-99 (Tc-99) decays following first order kinetics with k = 0116 h 1 How much Tc-99 remains after 22 hours in a solution initially 0500 M in Tc-99? A 0187 M B 0297 M C 0387 M D 0407 M Question #: 24 The decomposition below is second order in NO 2 How long will it take for the concentration of NO 2 to decrease from 400 M to 100 M? NO 2 (g) NO(g) + ½ O 2 (g) k = 34 M 1 min 1 A 088 min B 14 min C 022 min D 0074 min Question #: 25 When heated to 499 C, cyclopropane rearranges (isomerizes) and forms propene with a rate constant of min 1 What is the half-life of this reaction, in minutes? Report your answer to three significant figures Do NOT include units in your answer 1 minutes Question #: 26

24 The activation energy for a certain reaction is 255 kj and the ΔH rxn is 121 kj What is the activation energy of the reverse reaction? A 255 kj B 376 kj C 134 kj D 121 kj Question #: 27 A certain reaction has an activation energy of 254 kj/mol At what temperature will the reaction will proceed four times faster than it does at 298 K? A 294 K B 739 K C 302 K D 1190 K Question #: 28 In the diagram below, the 1 of the reaction is greater than the 2 needed to reach the 3 before proceeding to products Fill in the blanks with activation energy, enthalpy, or transition state

25 1 enthalpy 2 activation energy 3 transition state Question #: 29 Which two statements about catalysts are false? A A catalyst is a substance that lowers the activation energy of a chemical reaction B A catalyst is always an enzyme C A catalyst speeds up the rate of a reaction D A catalyst is consumed during the chemical reaction Question #: 30 The overall reaction 2O 3 (g) 3O 2 (g) can occur by the following mechanism: NO(g) + O 3 (g) NO 2 (g) + O 2 (g) O 3 (g) O 2 (g) + O(g) NO 2 (g) + O(g) NO(g) + O 2 (g) Select the TWO intermediates in this mechanism NO(g) + O 3 (g) NO 2 (g) + O 2 (g) A NO(g) B O 3 (g) C NO 2 (g) D O 2 (g) E O(g)