Concentration 0. 5 M solutions 1. 0 M solutions. Rates Fast Slow. Which factor would account for the faster reaction rate in Experiment 1?

Transcription

1 72. Consider the following experimental results: Experiment 1 Experiment aq Reactants Fe ( aq) + MnO4 ( aq) MnO ( aq) + H C O ( ) Temperature 20 C 40 C Concentration 0. 5 M solutions 1. 0 M solutions Rates Fast Slow Which factor would account for the faster reaction rate in Experiment 1? A. temperature B. surface area C. nature of reactants D. solution concentration 73. Consider the reaction: C5H12( g) + 8O2( g) $ 5CO2( g) + 6H2O( g) Which of the following explains, in terms of collision theory, why this reaction occurs in more than one step? A. a low C 5 H 12( g) concentration B. low temperature of reactant mixture C. low probability of a multi-particle collision D. particles collide with insufficient kinetic energy 74. Which of the following factors only affects the rate of heterogeneous reactions? A. nature of reactants B. presence of a catalyst C. temperature of reactants D. surface area of reactants

2 75. Consider the following reactions in open systems: I. 2H2( g) + O2( g) Æ 2H2O( g) II. CaCO3( s) Æ CaO( s) + CO2( g) III. CaO( s) + SiO2( s) Æ CaSiO3( s) IV. AgNO3( aq) + NaCl( aq) Æ NaNO3( aq) + AgCl( s) mass of system D time 4. Consider the following diagram: In which of the above could reaction rate be determined by D A. I B. II C. III D. IV 300? 76. Which of the following best describes activation energy? A. of activated complex B. of products of ( )- ( reactants) ( )- ( ) ( )- ( reactants) C. of reactants of activated complex D. of activated complex of Consider the following diagram: 300 Which of the following is true for the forward reaction? Reaction of Activated Complex kj ( ) DH kj ( ) A. catalyzed B. uncatalyzed C. catalyzed D. uncatalyzed Consider the following reaction: 2NO( g) + O2( g) Æ 2NO2( g) Why would this reaction probably involve more than one step?

3 78. Consider the following reaction: 2NO( g) + O2( g) Æ 2NO2( g) Why would this reaction probably involve more than one step? 79. A. There is insufficient activation energy. B. This reaction has high activation energy. C. Reactions between gases are typically slow. D. A successful collision between more than two molecules is unlikely. Consider the following reaction mechanism: Step 1 O3 Æ O2 + O Step 2 O3 + O Æ 2 O2 Which of the following could represent the activated complex for Step 2? A. O B. O 2 C. O 3 D. O 4 Use the following information to answer questions 80 and 81: When a candle ( C 20 H 42 ) burns, the following reaction occurs: 2C20H42( s) + 61O2( g) Æ 40CO2( g) + 42H2O( g) + heat If the rate of production of CO 2 is 0. 98g min, what is the rate of oxygen consumption? A g min B g min C g min D. 11. g min Which of the following properties could best be monitored in order to determine the reaction rate of the burning candle? A. mass of C H s ( ) B. pressure of H 2 O( g ) C. surface area of C 20 H 42 ( s ) D. concentration of C 20 H 42 ( s )

4 Which of the following is true of the kinetic and potential energies as reactant molecules approach each other to form an activated complex? 4. Which of the following KE are necessary for successful collisions between reactant molecules? A. increases decreases 4. Which of the following are necessary for successful collisi I. high concentration molecules? B. decreases increases II. sufficient energy C. decreases remains constant III. D. remains constant remains constant correct geometry IV. presence of a catalyst Which of the following are necessary for successful collisions between reactant molecules? A. I and II only B. I. II and high III only concentration C. III and IV only A. I and II only II. D. I, II and sufficient III onlyenergy B. II and III only III. correct geometry C. III and IV only D. I, II and III only IV. presence of a catalyst I. high concentration II. III. IV. sufficient energy correct geometry presence of a cataly Which of the following graphs most likely represents the slowest forward reaction? A Which of the following graphs most likely represents the s forward B. reaction? A B. C. D C D

5 85. For an exothermic reaction, which of the following is true? A. reactants > activated complex > products B. products > activated complex > reactants C. activated complex > reactants > products D. activated complex > products > reactants 86. Consider the following reaction: O( g) + O3( g) Æ 2 O2( g) Which of the following describes how the reaction s catalyzed diagram compares to the reaction s uncatalyzed diagram? E a A. E catalyzed E a DH ( ) < a unchanged ( ) > a unchanged ( ) < DH ( catalyzed) < D B. E catalyzed E a C. E catalyzed E a a ( ) < D. unchanged DH catalyzed DH H 87. Consider the following reaction mechanism: Step 1. NO + O3 Æ NO2 + O2 Step 2. O + NO2 Æ NO + O2 Which of the following substances is the catalyst? A. O B. O 2 C. NO D. NO Which of the following could represent the units for reaction rate? A. g ml B. g min C. g mol D. mol L

6 89. Consider the following reaction: Zn( s) + 2HCl( aq) Æ ZnCl2( aq) + H2( g) Which of the following would increase the reaction rate? A. an increase in pressure B. an increase in temperature C. an increase in the concentration of H 2 D. an increase in the concentration of ZnCl Consider the following reaction: H2( g) + I2( g) Æ 2HI( g) Which of the following is true of the activated complex relative to the reactants? KE Stability A. high stable B. low stable C. high unstable D. low unstable 91. Consider the following diagram: Which of the following is true for the forward reaction? DH kj ( ) of Activated Complex kj ( ) A B C D Which of the following could describe a catalyst? A. A substance that increases the reaction time. B. A substance that provides an alternate mechanism with a higher activation energy. C. A substance that is formed in one step and used up in a subsequent step in a reaction mechanism. D. A substance that is used up in one step and reformed in a subsequent step in a reaction mechanism.

7 93. The following forward reaction has an Ea = 167 kj : 28 kj + H2( g) + I2( g) Æ 2HI( g) Which of the diagrams below represents this reaction? A. B. 139 kj 167 kj C. D. 28 kj 195 kj Which of the following reactions is most likely to proceed at the greatest rate under standard conditions? A. Zn( s) + S( s) Æ ZnS( s) B. H2( g) + I2( g) Æ 2HI( g) C. Cu( s) + Cl2( g) Æ CuCl2( s) D. 2KOH( aq) + H2SO4( aq) Æ 2H2O( l) + K2SO4( aq) Nitrogen monoxide and hydrogen react according to the following equation: 2NO( g) + 2H2( g) Æ N2( g) + 2H2O( g) If the rate of hydrogen consumption is g min, what is the rate of nitrogen production? A g min B g min C. 12. g min D. 24. g min

8 96. A student placed 30. g of Mg into some HCl in two different experiments. In each case, it reacted according the following equation: Mg( s) + 2HCl( aq) Æ MgCl2( aq) + H2( g) In the first experiment, it took 3. 2minutes for all of the Mg to react. In the second experiment, it took 54. minutes for all of the Mg to react. Which of the following could account for the change in rate of the second experiment? A. A catalyst was added. B. The Mg was powdered. [ ] was decreased. C. The H 2 D. The temperature was decreased. 97. Which of the following would change the value of the activation energy for a heterogeneous reaction? A. adding a catalyst B. changing the surface area C. changing the temperature D. changing the average kinetic energy 98. Consider the following reaction: H2( g) + I2( g) Æ 2HI( g) As a molecule of H 2 approaches a molecule of I 2 on a collision course, how do the KE and change? KE A. increases decreases B. decreases increases C. decreases decreases D. increases increases 99. Which of the following reactions is endothermic? A. H2( g) + S( s) Æ H2S( g) + 20 kj B. 4Fe( s ) + 3O2( g )-821kJ Æ 2Fe2O3( s ) C. CO2( g) Æ C( s) + O2( g) DH =+393kJ D. N2( g) + 3H2( g) Æ 2NH3( g) DH =-92 kj

9 100. A reaction has the following mechanism: NO Æ N O Step Step 2 NO H2 Æ NO 2 + HO 2 Step 3 NO 2 + H2 Æ N2 + HO 2 Which of the following substances is a reaction intermediate? A. H 2 B. NO C. HO 2 D. NO Consider the following diagram: Which of the following is true of the reverse reaction? ( ) Ea( kj) DH kj A. catalyzed B. catalyzed C. uncatalyzed D. uncatalyzed

10 102. Consider the following reaction mechanism for the formation of NO 2. NO N O Step Step 2 Overall 2NO + O 2NO 2 2 a) Complete Step 2. (2 marks) b) Define the term reaction intermediate. (2 marks) c) Identify a reaction intermediate in the above mechanism. (1 mark) 103. An Alka-Seltzer tablet is added to water to produce carbon dioxide gas. The gas was collected using water displacement. The following data is recorded: Time (s) Volume of CO 2 (ml) a) Calculate the average rate of reaction for the formation of CO 2 gas for the times: i) 0 10 s ii) s b) Suggest a reason why the rate of reaction from 0 to s is slower than the rate from to s? c) The rate of reaction is not constant during the entire interval from to s. Describe the change in rate and explain a reason for the change.

11 104. The mass of a burning candle is monitored to determine the rate of combustion of paraffin. An accepted reaction for the combustion of paraffin is: 2 C28H58( s) + 85O2( g) 56 CO2( g) + 58 H2O( g) The following data is observed: Time (min) Mass of Candle (g) a) Calculate the average rate of consumption of paraffin in g min for the time interval to minutes. b) Calculate the rate of CO 2 production in mol min for the time interval to minutes Consider the following proposed reaction mechanism: Step 1 Fe + H O FeH O Step 2 FeH O FeOH + HO a) Write the overall reaction. Step 3 HO + H2O2 H2O + HO Step 4 FeOH + HO Fe + H O + O 2 2 b) Define the term catalyst and identify a catalyst in the above mechanism Consider the following reaction: C12H22O11( s) 11 H2O( g) + 12C( s) The rate of decomposition of C12H22O11 is mol min. What mass of C is produced in seconds?

12 Define the term activation energy. Consider the reaction: C2H4( g) + 3O2( g) 2CO2( g) + 2H2O( g) At certain conditions, mol CO 2 is produced in 2. 0 minutes. What is the rate of consumption of C 2 H 4 in g s? Define the term reaction mechanism. Consider the reaction: 2Al( s) + 6HCl( aq) 2AlCl3 ( aq) + 3H2( g) A g sample of PART Al reacts B: WRITTEN completely RESPONSE in excess HCl in s. What is the rate of production of H 2 in mol s? Value: 40 marks Suggested Time: 50 minutes 111. Using collision theory, give two reasons why reactions occur more rapidly at a INSTRUCTIONS: higher temperature. You will be expected to communicate your knowledge and understanding of chemical principles in a clear and logical manner Consider Your the reaction: steps and assumptions leading to a solution must be written in the spaces below the questions. Answers must include 2HOunits 2 ( l) where 2Happropriate 2( g) + Oand be given to the correct number of significant figures. 2( g) For questions involving calculations, The rate of production of O 2 is full marks will NOT be given for providing only an answer. mol s. How many seconds will it take to decompose g H2O? 1. Using the axes below, sketch a diagram for the reacting system where: (3 marks) 113. Define the term catalyst. DH =-30kJ mol 114. Using the axes below, E = 50 sketch kj mol a diagram for the reacting system where: a DH =-30kJ mol E a = 50kJ mol

13 115. Consider the following reaction mechanism: NO! N O Step Step 2 NO H2! NO 2 + HO 2 Step 3 NO 2 + H2! N2 + HO 2 a) Determine the overall reaction. b) Identify a reaction intermediate Consider the following reaction: 3Cu( s) + 8HNO3 ( aq) $ 3Cu( NO3) 2( aq) + 2NO( g) + 4H2O( l) A piece of copper is added to a nitric acid solution in an open beaker, allowing the NO g ( ) to escape. The following data was obtained: TIME (min) MASS OF BEAKER AND CONTENTS (g) Copper a) Calculate the reaction rate for the time period 2. 0 to 6. 0 min. b) Calculate the mass of copper consumed in the first 5 minutes Using collision theory, explain why reactions between two solutions occur more rapidly than reactions between two solids. Consider the following reaction in an open flask: CaCO3( s) + 2HCl( aq) $ CaCl2( aq) + H2O( l) + CO2( g) A g sample of CaCO3 ( s) is placed in the flask and HCl ( aq) is added. The reaction consumes HCl ( aq) at an average rate of mol min for min. What mass of CaCO 3( s) remains?

14 119. a) Write the equation for Step 3 in the following reaction mechanism. NO! N O Step Step 2 NO H2! NO 2 + HO 2 Step 3? Overall Reaction 2NO + 2H! N + 2H O b) Identify a reaction intermediate in the above mechanism Consider the following reaction: Mg( s) + 2HBr( aq) $ MgBr2( aq) + H2( g) + energy In terms of collision theory, describe how each of the factors below would influence the reaction rate. a) Increasing the concentration of HBr : b) Decreasing the temperature: c) Increasing the surface area of Mg : 121. Consider the following reaction mechanism: Step 1 NO( g) + O2( g) $ NO3 ( g) slow 2. Consider the following reaction mechanism: (2 marks) Step 2 NO3 ( g) + NO( g) $ 2NO2( g) Step 1 NO( g) + O2( g) $ NO3 ( g) slow Step 2 NO The overall reaction is exothermic. 3 ( g) + NO Sketch ( g) $ 2NO a 2 ( g) diagram on the axes below to describe the energy changes that occur as the reaction takes place. The overall reaction is exothermic. Sketch a diagram on the axes below to describe the energy changes that occur as the reaction takes place. 3. Consider the following equilibrium system: (3 marks)

15 The release of O 2 ( g ) resulting from the decomposition of bleach was measured in two different experiments. Data was collected and the following graph was drawn: Value: 30 marks INSTRUCTIONS Volume Value: 30 marks O 2 ( ml) 70 PART B: WRITTEN RESPONSE Experiment 1 60 Experiment Suggested 2 Time: 40 minutes 50 You are expected to communicate your knowledge and understanding of chemical principles 40 in a clear and logical manner. Your steps and assumptions leading to a solution 30 must be written in the spaces below the questions. Answers must include units where appropriate PART B: WRITTEN and be given RESPONSE to the correct number of significant figures. For questions 20 involving calculations, full marks will NOT be given for providing only an answer. Suggested Time: 40 minutes 10 INSTRUCTIONS You are expected to communicate your knowledge and understanding of chemical principles in a 1.0 clear and 2.0 logical 3.0 manner. 4.0 Your steps 5.0 and assumptions leading to a 1. Consider the following solution equilibrium: must be written Time in the (min) spaces below the questions. Answers must include units where appropriate and be given to the correct number of significant figures. a) Calculate the For average questions rate of involving + reaction calculations, for each experiment. full marks will NOT + Al be given for ( H2O) 4( OH) providing only an answer. Æ Al( H2O) ( OH) + H 2 ( aq) 3 3( s) ( aq) b) Identify a variable from Experiment 1 and how it was changed to produce the a) Some different HCl reaction ( aq ) is added rate for to Experiment the equilibrium. 2. Explain What happens using collision to the amount theory. of solid Al( H O) 3( OH) 3? Explain. (2 marks) 1. Consider the following equilibrium: + ( ) ( ) Æ ( ) ( ) + Al H2O 4 OH Al H2O OH H 2 ( aq) 3 3( s) ( aq) a) Some HCl( aq ) is added to the equilibrium. What happens to the amount of solid Al H O OH ( ) ( )? Explain. (2 marks) b) The HCl is added at time t 1 and equilibrium is re-established at time t 2. On the axis below, sketch what happens to the reverse reaction rate. + (2 marks) b) The HCl is added at time Reverse t 1 and equilibrium is re-established at time t 2. On the axis below, sketch Reaction what happens to the reverse reaction rate. Rate (2 marks) t 1 t 2 Reverse Reaction Rate Time t 1 t 2 Time

16 124. When solid sodium is placed in water at room temperature, an immediate, violent reaction occurs: 2Na( s) + 2H2O( l) Æ 2NaOH( aq) + H2( g) + energy a) Describe two methods that could be used to experimentally determine the rate of reaction. b) Would you expect the activation energy of this reaction to be high or low? Explain, using collision theory Consider the following overall reaction which is exothermic: 2NO( g) + O2( g) Æ 2NO2( g) a) Complete the proposed two-step reaction mechanism. Step 1 NO + NO Æ N 2 O 2 Step 2 b) Describe how adding a catalyst would affect the activation energy and DH for the overall reaction?

17 Multiple Choice Answers: 1 A 6 B 11 C 16 D 21 D 26 D 31 C 36 D 41 B 46 D 2 B 7 D 12 D 17 B 22 C 27 A 32 D 37 A 42 C 47 D 3 B 8 D 13 B 18 C 23 B 28 A 33 D 38 C 43 C 48 A 4 A 9 C 14 B 19 A 24 D 29 D 34 B 39 C 44 B 49 C 5 A 10 B 15 D 20 C 25 D 30 A 35 A 40 B 45 D 50 B 51 D 56 C 61 C 66 B 71 A 76 D 81 A 86 A 91 D 96 D 52 A 57 C 62 D 67 B 72 C 77 B 82 B 87 C 92 D 97 A 53 C 58 A 63 C 68 A 73 C 78 D 83 B 88 B 93 A 98 B 54 D 59 A 64 C 69 D 74 D 79 D 84 A 89 B 94 D 99 C 55 D 60 C 65 B 70 C 75 B 80 D 85 C 90 D 95 B 100 D 101 B Written solutions: 102. a) b) c) N2O2 + O2 2NO2 A species that is produced and then used up in a later step. NO a) i) vol 30. ml 00. ml ii) rate = = vol t s rate = = t 30. ml = = ml s ml s = s = ml s b) The surface area of the tablet increases as the tablet crumbles ml 3. 0 ml s s c) The rate decreases during the interval because the surface area decreases a) mass r = t b) 11. g = min = g min 1mol C H rate = g min g 3 = mol min 56 mol CO 2 mol C H

18 105. a) 2HO 2 2 2HO 2 + O2 b) Definition: A species which speeds up a reaction by providing a lower energy pathway. Catalyst: Fe mol C12H22O11 12 mol C Rate of C production = min 1mol C12H2O mol = min mol g Mass of C in s = 9. 0 s mol ( ) 1min min 60 s = 18g Activation energy is the minimum amount of energy required to form the activated complex from the reactants. rate of formation of CO mol = 20. min = mol min rate of consumption of C H = 1 2 rate of formation of CO = mol min mol C2H g = 60 s mol = gs A reaction mechanism is a series of steps that result in the overall reaction. 1mol mol Al = 10. 0g = mol Al 27. 0g mol H 2 rate = = mol Al = mol H change in moles time mol H = s 3 mol H2 2 mol Al 3 mol H2 = s There is a greater fraction of collisions with sufficient energy. 2 2 There are more frequent collisions.

19 112. 1mol mol H2O = g = mol g mol O = mol H O 2 2 1mol O2 2 mol H O = mol mol O mol time = = rate mol s = s 2 2. Consider the following reaction mechanism Step 1 2 Step 2 NO A catalyst is a substance that increases the rate of a chemical reaction and may be recovered at the end of the reaction. = 2. Consider the following reaction mechanism: a) 120 Calculate the reaction rate for the time period Solution: For Example: 80 0 Solution: Solution: ( mark for incorrect Progress significant of the reaction figures. ) Step 1 2NO! N2O2 1 mark for exothermic Step 2 NO H NO HO diagram ! Solution: Step 3 NO 2 +. to. min. (2 marks) a) Determine the overall reaction mark for mass change Step. 453 g- 188NO g+ H2! N2 + HO 2DH =-30kJ mol rate = = Overall Reaction: 2NO + 2H2! N2 + 2 time change ( ) min mark for g = E a = 50kJ 2 marks mol min a) Determine 20 the overall reaction. (2 marks) = 18. g min NO produced b) Identify a reaction intermediate. a) 10 Calculate the reaction rate for the time period 2. 0 to 6. 0 min. (2 marks) Deduct 1 2 Solution: For Example: 115. a) Overall Reaction: 2NO + 2H2! N2 + 2H2O b) œ 1 mark for reactants NO 2à 2 OR NO 2 1 mark for products 116. a) mass change g g rate b) Calculate = time change the mass = of ( copper consumed ) min in the first 5 minutes. (3 marks) Solution: g b) Identify = a reaction intermediate. 2 marks (1 mark) 40. min For Example: = 18. g min NO produced Solution: g g moles b) ( Deduct NO 1 NO produced = = mol NO 22 mark 2 OR forno incorrect significant g mol figures. 2 ) 1 mark 1mark 3 mol Cu moles Cu consumed = mol NO = mol Cu 2 mol NO 1 mark b) Calculate the mass of copper consumed in the first 5 minutes. (3 marks) Solution: gcu mass Cu consumed = mol Cu = 32. 1g Cu 1 mol Cu For Example: g g 1 mark

20 117. Particles must be able to collide to react. Only the particles on the surface of a solid are available for reaction. In a solution, all particles are available Amount of HCl reacting = mol min min = mol 1CaCO3 Moles of CaCO3 reacting = mol HCl =1. 00mol CaCO 2HCl g 2 Mass of CaCO3 reacting = mol CaCO3 = g 1mol Mass remaining = g g = 55g a) Step 3: N2O + H2 Æ N2 + H2O b) Either NO 2 2 OR NO a) b) c) 121. Greater concentration and more collisions. Therefore more successful collisions and a greater rate. Fewer collisions with sufficient energy to overcome barrier. Therefore, a lower rate. Increased surface area leads to more collisions and more successful collisions. Therefore, a higher rate. 1 2 mark for 2 humps 1 2 mark for first hump higher than second 1 mark for exothermic reaction b) Identify a variable from Experiment 1 and how it was changed to produ different reaction rate for Experiment 2. Explain using collision theory a) 60 ml Experiment 1: = 24 ml min 25. min b) 50 ml Experiment 2: = 11mL min 45. min Solution: For Example: Variable/Change Temperature is decreased. Concentration of reactants was decreased. 1mark 1mark OR Explanation Lower fraction of effective collisions. Fewer collisions. 3mar

21 123. a) b) The amount of solid decreases because the equilibrium shifts left. reverse Reverse Reaction Rate t 1 t 2 Time 124. a) Any two of the following per unit time: D mass Na D volume H 2 D temperature D ph D pressure b) 125. a) The reaction is very fast so many collisions at room temperature would have the needed energy to be successful. The activation energy of this reaction would be low. Step 1 NO + NO Æ N 2 O 2 Step 2 NO O2 Æ 2NO2 b) A catalyst provides a different mechanism with a lower E a. Catalyst has no effect on DH.