S11Q5W7 - CHEM 0120 Golde SPRING 2011 QUIZ 5 WEEK 7 Monday...

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CHEM 0120 SPRING 2011 Monday 1:00 PM Golde QUIZ 5 WEEK 7 February 14, 2011 Name_______________________________ G ° = H ° - T S ° , G ° = -RTln(K), R = 8.31 J/mol K, G = G o + RTln(Q) 1. For the reaction NH 4 Cl(s) NH 4 + (aq) + Cl - (aq) H o f (kJ/mol) -314.4 -133.3 -167.1 S o (J/mol K) +94.6 +111.2 +56.6 a) Calculate H o and S o for this reaction. b) Do you expect the temperature of the solution to increase or to decrease when solid NH 4 Cl is mixed with water? Give your reasoning. c) Calculate G o of this reaction at 25 o C. Watch your units! Do you expect NH 4 Cl to have a high solubility in water at 25 o C? Give your reasoning. ANSWERS 1. a) H o = [-167.1 -133.3] - [-314.4] kJ = +14.0 kJ S o = [111.2 + 56.6] - [94.6] J/K = +73.2 J/K b) The positive sign of H o indicates that the reaction is endothermic: the mixture will cool as NH 4 Cl is added to water. c) G o = 14000 J - 298K (73.2 J/K) = -7.81 kJ The negative sign indicates that this process is spontaneous and that NH 4 Cl is very soluble. CHEM 0120 SPRING 2011 Monday 6:00 PM Golde QUIZ 5 WEEK 7 February 14, 2011 For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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Name_______________________________ G ° = H ° - T S ° , G ° = -RTln(K), R = 8.31 J/mol K, G = G o + RTln(Q) 1. In each of the following pairs, state which species has the higher absolute entropy. Give your reasoning. a) CH 3 COOH(l) or CH 3 COOH(s) at the same temperature b) 1 mol of N 2 gas at 25 o C or 1 mol of N 2 gas at 100 o C 2. For the reaction: NH 4 + (aq) + OH - (aq) NH 3 (aq) + H 2 O(l) ΔH o = -3.59 kJ and ΔS o = +78.6 J/K (for the left-to-right direction of the reaction). a) Calculate ΔG o for this reaction at 50 o C. b) Which direction of this reaction is preferred under standard conditions at this temperature? Give your reasoning. ANSWERS 1. a) CH 3 COOH(l). Conversion of a solid to a liquid increases the randomness of the system and the number of possible arrangement of the molecules, so the entropy increases. b) The gas at 100 o C. Entropy increases with temperature. 2. a) ΔG o = -3590 J – 323K x 78.6 J/K = -2.90 x 10 4 J = -29.0 kJ b) As ΔG o < 0, the left-to-right direction is preferred. CHEM 0120 SPRING 2011 Tuesday 8:00 AM Golde QUIZ 5 WEEK 7 February 15, 2011 Name_______________________________ G ° = H ° - T S ° , G ° = -RTln(K), R = 8.31 J/mol K, G = G o + RTln(Q) For Make-up Only Regular recitation Day: Time: instructor: Quiz Score: Group score: Scores recorded by:
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1. We wish to calculate G o for the following reaction at 298K in two ways: H 2 PO 4 - (aq) H + (aq) + HPO 4 2- (aq), K c = 6.2 x 10 -8 H o f (kJ/mol) -1302.6 0 -1299.0 S o (J/mol K) 92.5 0 -33.5 a) Calculate G o of reaction at 298K from the given H o and S o data. b) Calculate
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This note was uploaded on 02/20/2011 for the course CHEM 110 taught by Professor Dr.huston during the Spring '06 term at Pittsburgh.

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S11Q5W7 - CHEM 0120 Golde SPRING 2011 QUIZ 5 WEEK 7 Monday...

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