Chem_126_2009_Common_3_1zz0aANSwers

Chem_126_2009_Common_3_1zz0aANSwers - Chem 126 Common 3...

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Chem 126 Common 3 Part I April, 24, 2009 ANSWERS 1. What is the oxidation state of manganese in 1 4 MnO - ? (a) 1 (b) 2 (c) 3 (d) 5 (e) 7 2. Which of the following compounds has the largest entropy? Careful (a) H 2 (g) (b) H 2 O (g) (c) H 2 O (l) (d) H 2 O (s) (e) SiO 2 (s) 3. What is the change in E, when 2.0 x 10 3 J of heat is lost and the system expands from 1.0 to 11.0 L against an external pressure of 1.4 atm. (1 L·atm = 101.3 J) (a) -3,400 J (b) -600 J (c) 3,400 J (d) 600 J (e) -2,000 J 4. For which of the following processes is the change spontaneous? (a) The change in entropy of the universe decreases. (b) At constant pressure, H sys > 0 (endothermic), S sys > 0 and T is very small. (c) At constant pressure, H sys > 0 (endothermic), S sys > 0 and T is very large. (d) Ln(Q/K eq ) > 0 (e) The voltage for the reaction < 0. ( 29 ( 29 ( 29 ( 29 3 3 -1 1 kJ/mol -239 -201 Jmol 127 240. o f o f CH OH l CH OH g H S K - 5. Calculate the boiling point of methanol (CH 3 OH). (a) 0.336 K (b) 1198 K (c) 348 K (d) 342 K (e) 336 K 6. Calculate the approximate vapor pressure of methanol at 300 K. (a) 0.022 atm (b) 0.19 atm (c) 0.50 atm (d) 0.29 atm (e) > 1 atm 0 for very large T sys sys sys G H T S = ∆ - ∆ < ( 29 ( 29 ( 29 3 1.64 38,000 / 300 113 / / 4,100 / ln 4,100 ln 1.64 8.314 300 0.19 o o o eq o eq CH OH eq G H T S J mol K J mol K J mol G RT K J G mol K J RT K mol K P K e atm - = ∆ - ∆ = - = = - = - = - = - = = = ( 29( 29 101.3 1.4 11 1 14 1,400 2,000 1400 3,400 ext J w P V atm L L atm J L atm E q w J J = - = - - = - = - = + = - - = - Gases generally have larger entropies than liquids which have larger entropies than solids. The larger the moleule and the more complicated the molecule the larger the entropy. ( 29 201 239 38 / 240 127 113 / / 38,000 / 0 at boiling point; T= 336 113 / / o o o o o o o H kJ mol S J mol K H J mol G H T S K S J mol K = - - - = = - = = = ∆ - ∆ = = ( 29 2, : 4 2 1; 7 O Mn x x x = - = + - = - =
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7. Calculate the change in entropy for the following reaction: N 2 H 4 (l) + 2O 2 (g) 2NO 2 (g) + 2H 2 O (l ) ( 29 / / : 121 205 240 70 o f S J mol K (a) 86 Jmol -1 K -1 (b) -16 Jmol -1 K -1 (c) 16 Jmol -1 K -1 (d) -89 Jmol -1 K -1 (e) 89 Jmol -1 K -1 8. 100 J is added to 2.0 grams of iron.
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This note was uploaded on 11/09/2010 for the course CHEM Chem taught by Professor Petrova during the Spring '09 term at NJIT.

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Chem_126_2009_Common_3_1zz0aANSwers - Chem 126 Common 3...

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