Exam III Solutions

Exam III Solutions - MIT OpenCourseWare http:/ocw.mit.edu...

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MIT OpenCourseWare http://ocw.mit.edu 5.111 Principles of Chemical Science Fall 2008 For information about citing these materials or our Terms of Use, visit: http://ocw.mit.edu/terms .
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Page 1 of 10 pages Third Hour Exam 5.111 Write your name below. This is a closed book exam. Solve all 6 problems. Read all problems thoroughly and read all parts of a problem. Many of the latter parts of a problem can be solved without having solved earlier parts. Show all work to receive full credit. Physical constants, formulas, standard reduction potentials, and a periodic table are given on the last two pages of the exam. You may detach the last 2 pages after the exam has started. 1. THERMODYNAMICS (12 points)___________ 2. CHEMICAL EQUILIBRIUM (12 points)___________ 3. ACID-BASE EQUILIBRIUM (12 points)___________ 4. ACID-BASE TITRATION (22 points)______________ 5. OXIDATION/REDUCTION (30 points)_____________ 6. OXIDATION/REDUCTION (12 points)_____________ Total (100 points)_____________ Name____ANSWER KEY__________________
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Page 2 of 10 pages 1. THERMODYNAMICS (14 points total) Consider the formation of MgO (s). Assume that Δ H r ° and Δ S r ° are independent of temperature. Mg (s) + 1/2 O 2 (g) MgO (s) Δ H r ° = -602 kJ/mol Δ S r ° = -108 JK -1 mol -1 . (a) (6 points) Calculate Δ G r ° for the formation of MgO (s) at 0 ° C (273 K). Is the reaction spontaneous or non-spontaneous at 0 ° C? Δ G = Δ H - T Δ S Δ G = -602 kJ/mol - 273(-0.108 kJmol -1 K -1 ) + 2 9 . 4 8 Δ G = -572 .52 - 573 kJ/mol spontaneous (b) (6 points) Is there a temperature at which the formation of MgO switches from spontaneous to non- spontaneous or vice versa? If no, explain briefly why not. If yes, calculate the temperature (T*) at which the spontaneity of the reaction switches. Yes. 0 = Δ H – T* Δ S T* = Δ H / Δ S T* = -602 kJ/mol - 0.108 kJ/mol K T* = 557 4 K T* = 5570 K
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Page 3 of 10 pages 2. CHEMICAL EQUILIBRIUM (12 points total) Explain the effect of each of the following stresses on the position of the following equilibrium: 3 NO (g)
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This note was uploaded on 09/25/2010 for the course BIOLOGY Biology 10 taught by Professor D'arville during the Spring '10 term at Rutgers.

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Exam III Solutions - MIT OpenCourseWare http:/ocw.mit.edu...

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