quiz3 - of Cl 2(g given the following 2 K(s Cl 2(g 2 KCl(s...

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CHEM 2046 QUIZ 3 FALL 2007 1. (8 points) Indicate whether there is an increase or decrease in entropy for each of the following reactions or processes. N 2 (g) + O 2 (g) N 2 O 2 (g) ∆S < 0 I 2 (s) I 2 (g) ∆S > 0 Smoking a cigarette ∆S > 0 2 Al (s) + 3 Cl 2 (l) 2 AlCl 3 (g) ∆S > 0 2. (8 points) Circle the one having higher entropy assuming the same temperature. a) O 2 (g) Vs O 3 (g) b) NH 3 (g) Vs PH 3 (g) c) Br 2 (g) Vs Br 2 ( l) d) Pure graphite crystal Vs Impure Graphite crystal 3. (18 points) Fill in the blank with the appropriate words or phrases The __ 1st ____ law of thermodynamics states that energy can be neither created nor destroyed, but can only be ___ converted from one form to another __. The __ 3rd _____ law of thermodynamics states that the ___ entropy_ ___ of a pure crystalline solid is __ zero ______ at ___ 0 K ____. The __ 2nd_ ___ law of thermodynamics states that for any spontaneous process, the ____ entropy ______ of the universe must ___ increase_ _____.
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4. (6 points) Calculate the standard entropy, S
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Unformatted text preview: , of Cl 2(g) given the following: 2 K (s) + Cl 2(g) 2 KCl (s) ∆S 0 = - 187.22 J K-1 mol-1 S (K (s) ) = 64.63 J K-1 mol-1 S (KCl (s) ) = 82.56 J K-1 mol-1 ∆S rxn = 2x S (KCl (s) ) – { 2x S (K (s) ) + S (Cl 2(g) )} Solving: S (Cl 2(g) ) = 223.08 J K-1 mol-1 5. (10 points) Consider the following reaction N 2 (g) + O 2 (g) 2NO (g) . a) If ∆H 0 = 180.58 kJ and ∆S = 24.8 J K-1 , calculate ∆G at 200 K. ∆G 0 = ∆H- T∆S = 180.58 kJ – (200 K) x (24.8x10-3 kJ K-1 ) = 175.62 kJ b) This reaction switches from being spontaneous to being non spontaneous at a particular temperature called the crossover temperature. Complete the following statement by circling the correct choices: The reaction is spontaneous at low / high temperatures, and non spontaneous at low / high temperatures. c) Calculate the crossover temperature Set ∆ G 0 = 0 T= ∆H / ∆S = 180.58 x 10 3 J / 24.8 J K-1 = 7281 K...
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