Chemistry Exam II Form A, Exams of Chemistry

Download Chemistry Exam II Form A and more Exams Chemistry in PDF only on Docsity! 1 Chemistry 112 Name _______________________ Exam II Form A Section _______________________ June 18, 2007 Student No. _______________________ 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). 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. 2 Chem 112 - Exam 2 FORM A June 18, 2007 ---------------------------------------------------------------------------------------------------------------- 1. Which one of the following substances would have the largest absolute entropy at 25ºC and 1 atm pressure? A. He(g) B. H2O(s) C. Ne(g) D. C(s) E. SO2(g) ---------------------------------------------------------------------------------------------------------------- 2. Which one of the reactions below has a negative !S? A. 2SO2(g) + O2(g) " 2SO3(g) B. NH4Cl(s) " NH3(g) + HCl(g) C. PbCl2(s) " Pb 2+ (aq) + 2Cl!(aq) D. 2C(s) + O2(g) " 2CO2(g) E. H2O(l) " H2O(g) ---------------------------------------------------------------------------------------------------------------- 3. In the Haber process, ammonia is synthesized from nitrogen and hydrogen: N2 (g) + 3H2 (g) 2NH3 (g) !G° at 298 K for this reaction is !33.3 kJ/mol. What is the value of !G at 298 K for a reaction mixture that consists of 1.9 atm N2, 1.6 atm H2, and 0.65 atm NH3? A !1.8 kJ/mol B !3.86 # 10 3 kJ/mol C !7.25 # 10 3 kJ/mol D !104.5 kJ/mol E !40.5 kJ/mol ---------------------------------------------------------------------------------------------------------------- 3 ---------------------------------------------------------------------------------------------------------------- For questions 4 and 5 consider the following table of thermodynamic data. All values are tabulated for 25ºC. Substance !Gºf(kJ/mol) Sº(J/mol • K) C2H2(g) 209 201 C2H4(g) 68 219 C2H6(g) !33 230 H2O(g) !229 189 C2H5OH(%) !175 161 ------------------------------------------------------------------ 4. Determine the value of !Gº (in kJ/mol) for the following reaction taking place at 25ºC. C2H4(g) + H2O(g) " C2H5OH(%) A. !14 kJ/mo1 B. !472 kJ/mo1 C. !122 kJ/mo1 D. !336 kJ/mo1 E. 122 kJ/mo1 ------------------------------------------------------------------ 5. The value of !Sº for the following reaction is !233 J/mo1 K at 25ºC. What is the entropy (in J/mo1 • K) of H2(g) at 25ºC? C2H2(g) + 2H2(g) " C2H6(g) A. 29 J/mo1 • K B. 204 J/mo1 • K C. 102 J/mo1 • K D. 262 J/mo1 • K E. 131 J/mo1 • K ---------------------------------------------------------------------------------------------------------------- 4 ---------------------------------------------------------------------------------------------------------------- 6. For a given reaction, "H = + 35.5 kJ/mol and "S = + 83.6 J/K-mol. Which statement is true? Assume that "H and "S do not vary with temperature. A. The reaction is spontaneous at T < 425 K B. The reaction is spontaneous at T > 425 K C. The reaction is spontaneous at all temperatures D. The reaction is spontaneous at T > 298 K E. The reaction is spontaneous at T < 298 K ---------------------------------------------------------------------------------------------------------------- 7. What is the value of "G° for the following reaction at 25 °C? HOCN H + (aq) + OCN!(aq) Ka = 3.5 # 10 !4 A. !17.7 kJ/mol B. !8.56 kJ/mol C. !3.46 kJ/mol D. 7.96 kJ/mol E. 19.7 kJ/mol ---------------------------------------------------------------------------------------------------------------- 8. Which substance is serving as the reducing agent in the following reaction? 14H + (aq) +Cr2O7 2$ (aq) + 3Ni(s) " 3Ni 2+ (aq) + 2Cr 3+ (aq)+ 7H2O(%) A. H + (aq) B. Ni(s) C. Ni 2+ (aq) D. Cr2O7 2$ (aq) E. H2O(%) ----------------------------------------------------------------------------------------------------------------