C117 Practice Exam 2 Fall 2024 PDF

C117 Practice Exam 2 Fall 2024 Chemical Kinetics (Ch 14) Sections (14.4-14.12) Equilibrium (Ch 15) Sections 15.1-15.5 Kinetics Equations: − Ea / RT =k Ae = ( where A...

C117 Practice Exam 2 Fall 2024 Chemical Kinetics (Ch 14) Sections (14.4-14.12) Equilibrium (Ch 15) Sections 15.1-15.5 Kinetics Equations: − Ea / RT =k Ae = ( where A pZ ) R = 8.314 J/K·mol  E  1   k  − Ea  1 1  ln k =  − a   + ln A ln  2  =  −   R  T   k1  R  T2 T1  Reaction Half-Life Integrated Rate Law Order Expression [ A ]0 zero [A]t = −kt + [A]0 t 12 = 2k ln[A]t = −kt + ln[A]0 or 0.693 first t 12 = k  [A]t  ln   = −kt  [A]0  1 1 1 second = kt + t 12 = [ A ]t [ A ]0 k [ A ]0 Equilibrium Equations: Latm c ( RT ) R 0.08206 760 torr = 1 atm ∆n Kp K= molK Quadratic Equation 𝑎𝑎𝑎𝑎 2 + 𝑏𝑏𝑏𝑏 + 𝑐𝑐 = 0 −𝑏𝑏 ± √𝑏𝑏2 − 4𝑎𝑎𝑎𝑎 𝑥𝑥 = 2𝑎𝑎 1 1. Sucrose, a sugar, decomposes in acidic solution to produce glucose and fructose. The reaction is first order in sucrose and at 25°C the rate constant is: k = 3.60 ×10−3 h −1. If the initial concentration of sucrose is 0.050 M, what is the concentration after 2 days? a) 0.013 M b) 0.028 M c) 4.3 × 10−3 M d) 0.042 M 2. The gas phase decomposition of HI has the following rate law. 2 HI( g )  → H 2 ( g ) + I2 ( g ) Rate = k[HI]2 3. At 443°C, k = 30.1 M −1 min −1. If the initial concentration of HI is 0.010 M, what is the concentration after 1.5 hours? −3 a) 6.9 ×10 M −3 b) 1.8 ×10 M −4 c) 3.6 ×10 M −4 d) 8.9 ×10 M 4. For the zeroth-order reaction: A → products, what will happen to the rate of reaction if the concentration of A is tripled? a) The rate will equal the original rate raised to the power of 3. b) The rate will be tripled. c) The rate will be one-third. d) The rate will remain the same. 5. Reaction of the anticancer drug cisplatin, Pt(NH3)2Cl2, with water is described by the equation: Pt(NH3)2Cl2 (aq) + H2O (l) → Pt(NH3)2(H2O)Cl+ (aq) + Cl– (aq) The rate of this reaction increases by a factor of 15 on raising the temperature from 25 °C to 50 °C. Which equation indicates the correct set up to solve for activation energy?  15  Ea  1 1  a) ln   = −  −  1 (8.314 J/mol ⋅ K)  25 50  1 Ea  1 1  b) ln   = −  −   15  (8.314 J/mol ⋅ K)  50 25  2  1 Ea  1 1  c) ln   = −  −   15  (8.314 J/mol ⋅ K)  323 298   15  Ea  1 1  d) ln   = −  −  1 (8.314 J/mol ⋅ K)  323 298  6. If a certain reaction has a rate constant of 9.51 × 10–9 L mol–1 s–1 at 500 K and a rate constant of 1.10 × 10–5 L mol–1 s–1 at 600 K, what is the value for Ea? a) 1.00 x 102 kJ/mol b) 1.76 x 102 kJ/mol c) 6.85 x 103 kJ/mol d) 1.72 x 105 kJ/mol 7. The values Ea = 248 kJ/mol and ΔE = 41 kJ/mol have been measured for the reaction H2 ( g ) + CO2 ( g ) → H2O(g ) + CO(g ). What is the value of Ea and ΔE for the reaction H 2O(g ) + CO(g ) → H 2 ( g ) + CO2 ( g ) ? a) Ea = – 248 kJ/mol, ΔE = 41 kJ/mol b) Ea = 248 kJ/mol, ΔE = – 41 kJ/mol c) Ea = 289 kJ/mol, ΔE = – 41 kJ/mol d) Ea = 207 kJ/mol, ΔE = – 41 kJ/mol 8. Why does the rate of a chemical reaction increase when a catalyst is added? a) The catalyst provides an alternate mechanism with a lower activation energy. b) The catalyst lowers the energy of the products. c) The catalyst increases the collision frequency of the reactants. d) The catalyst increases the energy of the collisions. e) All of the above 3 To answer questions 8–11, refer to the mechanism: H 2 O 2 (aq ) + I − (aq )  → OH − (aq ) + HOI(aq ) slow HOI(aq ) + I − (aq )  → OH − (aq ) + I 2 (aq ) fast 2 OH − (aq ) + 2 H 3O + (aq )  → 4 H 2 O(l ) fast 8. What is the overall reaction? a) H2O2 (aq) + 2 I– (aq) + 2 H3O+ (aq) → I2 (aq) + 4 H2O (l) b) H2O2 (aq) + 2 I– (aq) → I2 (aq) + 4 H2O (l) c) 2 H2O2 (aq) + 2 I– (aq) → I2 (aq) + 4 H2O (l) d) H2O2 (aq) + I– (aq) + H3O+ (aq) → I2 (aq) + 4 H2O (l) 9. Identify the intermediate(s) and catalyst in the mechanism. a) Catalyst = I– Intermediates = OH–, HOI b) Catalyst = H3O+, Intermediate = HOI c) No catalyst, Intermediate = I2 d) No catalyst, Intermediates = OH–, HOI 10. What is the rate law for the reaction? a) Rate = k[H2O2][I–]2 b) Rate = k [H2O2][I–] c) Rate = k [H2O2][I–]2 [H3O+]2 d) Rate = k [H2O2]2[I–] e) Rate = k [H2O2]2[I–]2 4  11. Select the correct potential energy diagram for the mechanism. The reaction is exothermic. 12. The following mechanism has been proposed for the oxidation to nitric oxide to nitrogen dioxide. NO (g) + O2 (g) ⇌ NO3 (g) Faster NO3 (g) + NO (g) →2 NO2 (g) Slower What is the rate law for this mechanism? a) Rate = k [NO3][NO] b) Rate = k [NO][O2] c) Rate = k [NO3]2[NO] d) Rate = k [NO]2[O2] 5  13. Which of the following statements about dynamic equilibrium is FALSE? a) The concentration of the reactants are equal to the concentration of the products. b) The concentration of the reactants and products are constant. c) The rate of the forward reaction is equal to the rate of the reverse reaction. d) When Kc =0.002, the concentration of reactants is greater than the concentration of the products. 14. Hydrogen is synthesized by the following reaction: CO(g) + H2O(g) ⇌ CO2(g) + H2(g) The diagram shows how the concentrations of H2O (g) and H2(g) change with time. At which point is equilibrium first reached? a) A b) B c) C d) D e) E 15. The following pictures represent mixtures of A2B4 molecules and AB2 molecules, which interconvert according to the equation A2B4 ⇌ 2 AB2. If mixture (1) is at equilibrium, which of the other mixtures are also at equilibrium? a) mixture (2) b) mixture (3) c) mixture (4) d) None of the other mixtures are at equilibrium. e) All of the mixtures are at equilibrium. 6  16. Nitrogen dioxide decomposes to nitric oxide and oxygen: 2 NO2(g) ⇌ 2 NO(g) + O2(g), Kc = 5.63 ×10−2 What is the equilibrium concentration of NO2 if the equilibrium concentration of O2 is 0.132 M, and NO is 0.108 M at a certain temperature? a) 0.273 M b) 0.074 M c) 0.367 M d) 0.165 M 17. What is the equilibrium constant expression (Kc) for the reaction below? Na2O2 (s) ⇌ 2 Na (l) + O2 (g) [Na]2 [O 2 ] a) K c = [Na 2 O 2 ] b) K c = [Na]2 [O 2 ] c) K c = [O 2 ] [Na][O 2 ] d) K c = [Na 2 O 2 ] 18. For the reaction 2 N2 (g) + 6 H2 (g) ⇌ 4 NH3(g), Kp = 4.4 × 10–7 at 400°C. What is the value of Kp for the reaction, 2 NH3(g) ⇌ N2(g) + 3 H2(g), a) 3.3 × 10-4 b) 5.2 × 1012 c) 2.3 × 106 d) 1.5 × 103 7  19. For the gas-phase reaction  2 SO3 (g) 2 SO 2 ( g ) + O 2 ( g )  5.8 ×103 at 600°C Kc = Predict the direction in which the reaction will proceed to reach equilibrium if the initial concentrations are [SO2] = 0.010 M, [O2] = 0.010 M, [SO3] = 0.200 M. a) The reaction will shift to produce more SO3. b) The reaction will shift produce more SO2 and O2. c) The reaction is at equilibrium and will not shift in either direction 20. At a temperature of 430°C, the reaction H2 (g) + I2 (g) ⇌ 2 HI (g) has an equilibrium constant (Kc) of 54.3. Suppose a non-equilibrium mixture contains 0.100 M H2(g), 0.100 M of I2(g) and 1.50 M HI (g). Identify the correct mathematical expression for solving for x in the ICE table. (1.50 − 2 x) 2 a) = 54.3 (0.100 + x)(0.100 + x) (1.50 + 2 x) 2 b) = 54.3 (0.100 − x)(0.100 − x) (1.50 − x) 2 c) = 54.3 (0.100 + x)(0.100 + x) (2 x) 2 d) = 54.3 (0.100 − x)(0.100 − x) 21. Refer to problem 20. Calculate the concentration of HI(g) when equilibrium is reached. a) 1.08 M b) 1.34 M c) 0.764 M d) 0.285 M 8  22. Consider the reaction and the associated equilibrium constant A2 (g) ⇌ 2 A(g) Kc = 5.1 Initially, A2 is added to the flask with a concentration of 0.500 M. Identify the correct mathematical expression for solving for x in the ICE table. (2 x) 2 a) = 5.1 (0.5 + x) (2 x) b) = 5.1 (0.5 − x) (2 x) 2 c) = 5.1 (0.5 − x) 2 (2 x) 2 d) = 5.1 (0.5 − x) 23. Refer to problem 22. Calculate the concentration of A2 (g) when equilibrium is reached. a) 0.116 M b) 0.384 M c) 0.768 M d) 0.043 M 24. Calculate the value of the equilibrium constant Kp at 298 K for the reaction:  N 2 ( g ) + 2 O 2 ( g ) 2 NO 2 (g)  ? Kp = Given the following data at 298 K.  2 NO(g) N 2 ( g ) + O 2 ( g )  4.4 ×10−31 Kp = 1  NO 2 (g) NO( g ) + O 2 ( g )  1.5 ×106 Kp = 2 a) K= p 6.6 ×1025 b) K= p 1.0 ×1018 c) K= p 9.9 ×10−19 d) K= p 5.4 ×10−28 9  25. Bonus (3 pts.) What is the equilibrium constant, Kc, for the reaction below? 2 Hg(l) + O2(g) ⇌ 2 HgO(s) The reaction is contained in a 1.0 L flask and at equilibrium the following amounts are present. 1.00 g of HgO(s), 2.00 mL of Hg(l), and 51.2 g O2(g)? (The molar mass and density of HgO(s) is 217 g/mol, and 1.10 g/cm3. The molar mass and density of Hg(l) is 201 g/mol, and 13.6 g/mL.) a) 6.85 × 10–4 b) 4.66 × 10–2 c) 0.625 d) 1.46 × 103 10  Short Answer: 1. (The first-order reaction, 2 N2O (g)→ 2 N2(g) + O2(g), has a half-life equal to 3.40 seconds at 750 K. How long will it take (in seconds) for the concentration of N2O to decrease to 38% of its initial concentration? 11  2. Consider the reaction that occurs in one step. 2 HI (g) → H2 (g) + I2 (g) a) Do all collisions of two HI molecules lead to a chemical reaction? Explain. b) Sketch the orientation of two HI molecules approaching one another in an orientation that will lead to an effective collision. (a collision that results in a reaction). c) The reaction has Ea = 183 kJ/mol and ΔE = 9 kJ/mol. Sketch a potential energy diagram for the reaction. Potential energy on the y axis and reaction progress on the x axis. Label the activation energy, the transition state, the reactants, and products. d) On diagram above draw a new potential energy curve if a catalyst is added and the reaction occurs by a different two-step mechanism. (Label the curve representing the catalyst.) 12 3. Consider the reaction: H2O (g) + CH4 (g) ⇌ CO (g) + 3 H2 (g) Initially, the reactants were added to the flask with concentrations of [H2O] = 0.070 M and [CH4] = 0.050 M. After equilibrium was reached the concentration of CO (g) was 0.025 M. Calculate the equilibrium constant (Kc) for this reaction at the given temperature. 13  1A 8A 1 18 1 2A 3A 4A 5A 6A 7A 2 H 2 13 14 15 16 17 He 1.01 4.00 3 4 5 6 7 8 9 10 Li Be B C N O F Ne 8B 6.94 9.01 10.8 12.0 14.0 16.0 19.0 20.2 11 12 3B 4B 5B 6B 7B 1B 2B 13 14 15 16 17 18 Na Mg 3 4 5 6 7 8 9 10 11 12 Al Si P S Cl Ar 23.0 24.3 27.0 28.1 31.0 32.1 35.4 39.9 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Ga Ge As Se Br Kr 39.1 40.1 45.0 47.9 50.9 52.0 54.9 55.8 58.9 58.7 63.5 65.4 69.7 72.6 74.9 79.0 79.9 83.8 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 Rb Sr Y Zr Nb Mo Tc Ru Rh Pd Ag Cd In Sn Sb Te I Xe 85.5 87.6 88.9 91.2 92.9 95.9 (98) 101 103 106 108 112 115 119 122 128 127 131 55 56 57 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 Cs Ba La Hf Ta W Re Os Ir Pt Au Hg Tl Pb Bi Po At Rn 133 137 139 178 181 184 186 190 192 195 197 201 204 207 209 (209) (210) (222) 87 88 89 104 105 106 107 108 109 Fr Ra Ac Rf Ha Unh Uns Uno Une (223) 226 227 (261) (262) (263) (262) (265) (266) 14