Chemistry Exam: Thermodynamics and Redox Reactions, Exams of Chemistry

Download Chemistry Exam: Thermodynamics and Redox Reactions and more Exams Chemistry in PDF only on Docsity! Chemistry 112 Name _______________________ Exam III Form A Section _______________________ April 8, 2009 eMail _______________________ IMPORTANT: On the scantron (answer sheet), you MUST clearly fill your name, your student number, section number, and test form (white cover = test form A; yellow cover = test form B). Use a #2 pencil. There are 25 questions on this exam. Check that you have done all of the problems and filled in the first 25 bubbles on the scantron. The maximum score on this exam is 25 points. Your score will be reported in percent (max 100%). Exam policy • Calculators with text-programmable memory are not allowed. • Relevant data and formulas, including the periodic table, are attached at the end of this exam. • Your grade will be based only on what is on the scantron form. • The answer key will be posted on the web after the exam (on the Exam Schedule page). • You must turn in your cover sheet with your scantron answer form. Hints • As you read the question, underline or circle key words to highlight them for yourself. Avoid errors from "mis-reading" the question. • Pay attention to units and magnitudes (decimal places) of numbers obtained from calculations. • There is no penalty for guessing. ------------------------------------------------------------------------------------------------------------ 7. Which of the following reactions will have a formation constant (Kf) with the largest value? A. [Co(H2O)6]2+(aq) + 6 L (aq)  [Co(L)6]2+(aq) + 6 H2O(l) where L = NH3 B. [Co(H2O)6]2+(aq) + 6 L (aq)  [Co(L)6]2+(aq) + 6 H2O(l) where L = C. [Co(H2O)6]2+(aq) + 6 L (aq)  [Co(L)6]2+(aq) + 6 H2O(l) where L = D. [Co(H2O)6]2+(aq) + 3 L (aq)  [Co(L)3]2+(aq) + 6 H2O(l) where L = E. [Co(H2O)6]2+(aq) + 2 L (aq)  [Co(L)2]2+(aq) + 6 H2O(l) where L = ------------------------------------------------------------------------------------------------------------ NH2 CH2 CH3 OH CH2 CH3 NH2 CH2 CH2 NH2 NH2 CH2 CH2 NH CH2 CH2 NH2 ------------------------------------------------------------------------------------------------------------ 8. The standard enthalpy change of fusion (melting), ΔH°fusion, of substance X is +35 kJ/mol at 1 atm pressure. The melting temperature of substance X is 42°C at 1 atm pressure. What is the standard entropy change of fusion, ΔS°fusion ? (Assume that ΔH°fusion and ΔS°fusion don’t change with temperature) A. 0 J mol−1 K−1 B. −33 J mol−1 K−1 C. 87 J mol−1 K−1 D. 111 J mol−1 K−1 E. 48 J mol−1 K−1 ------------------------------------------------------------------------------------------------------------ 9. Hydrometallurgy involves leaching a metal from an ore by selectively dissolving it, then obtaining the free metal by reduction. One such example is Au, which can be leached from an ore with cyanide to form a soluble Au(CN)2– complex. The standard reduction potential (E°) for Au(CN)2– is –0.6 V and corresponds to the reaction below: Au(CN)2– (aq) + e–  Au + 2 CN–(aq) E° = –0.6 V Which of the following metals could be used to reduce Au(CN)2– to Au metal? (i) Pd E° = 0.9 V for Pd2+ + 2 e–  Pd (ii) Mg E° = –2.4 V for Mg2+ + 2 e–  Mg (iii) Fe E° = –0.4 V for Fe2+ + 2 e–  Fe A. (i) only B. (ii) only C. (iii) only D. (i) and (ii) E. (ii) and (iii) ------------------------------------------------------------------------------------------------------------ Go on to the next page ------------------------------------------------------------------------------------------------------------ 10. Which of the following crystal field splitting diagrams represents a strong-field octahedral complex of Fe3+? (Note: The diagrams do not represent the relative magnitudes of Δ.) A. B. C. D. E. ------------------------------------------------------------------------------------------------------------ Go on to the next page ------------------------------------------------------------------------------------------------------------ 18. A plot of ΔH and TΔS for a reaction as a function of temperature is shown below. Based on this plot, which one of the statements is true if ΔG° for the reaction is positive? A. ΔH is positive and ΔS is negative B. ΔH is negative and ΔS is positive C. ΔH is positive and ΔS is positive D. ΔH is negative and ΔS is negative E. None of the above ------------------------------------------------------------------------------------------------------------ 19. Which of the following octahedral coordination compounds contains a transition metal with three unpaired d electrons? Note: CN– is a strong field ligand, and F–, Cl–, Br–, and NH3 are weak field ligands. A. K4[Ni(CN)6] B. K3[Co(CN)6] C. Na3[CoBr6] D. Na4[CoF6] E. [Ni(NH3)4Cl2] ------------------------------------------------------------------------------------------------------------ 500K Temperature Energy Go on to the next page ------------------------------------------------------------------------------------------------------------ 20. The value of ΔG° for the following reaction is −41.25kJ/mol. Ag+(aq) + 2NH3 ↔ [Ag(NH3)2]+(aq) Kf = 1.7× 107 At 25°C, what is ΔG for this process if the [Ag+] = 0.0100M, [NH3] = 0.00200M and [Ag(NH3)2+]= 0.00500M A. +29.1 kJ/mol B. +13.7 kJ/mol C. −13.7 kJ/mol D. −27.6 kJ/mol E. −12.2 kJ/mol ------------------------------------------------------------------------------------------------------------ 21. ΔG°f of liquid ethanol (C2H5OH) at 25 °C is −174.76 kJ/mol. ΔG°f of gaseous ethanol at 25°C is −168.5 kJ/mol. What is the equilibrium constant Keq for the vaporization of ethanol at 25 °C? C2H5OH (l) ↔ C2H5OH (g) A. 4.3 B. 0.080 C. 1.8 × 10−5 D. 7.4 × 108 E. 0.37 ------------------------------------------------------------------------------------------------------------ Go on to the next page ------------------------------------------------------------------------------------------------------------ 22. What is the equilibrium constant for the following balanced reaction at 25°C under standard state conditions? 2H2O(l) + Mg(s) → H2(g) + Mg(OH)2(aq) A. 2.33 × 1023 B. 9.01 × 10−5 C. 1.25 × 1052 D. 5.66 × 103 E. 1.26 × 1026 ------------------------------------------------------------------------------------------------------------ 23. What is the concentration of AgNO3(aq) in a voltaic cell built using the following unbalanced spontaneous redox reaction if [Al3+] = 1.5 M and Ecell = 2.44V at 25°C? Ag+ (aq) + Al(s) → Ag(s) + Al3+ (aq) A. 0.52 M B. 0.08 M C. 2.6 M D. 3.2 × 10−3 M E. 4.6 M ------------------------------------------------------------------------------------------------------------ Go on to the last page