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Make up Test 3-solutions

# Make up Test 3-solutions - Version 095 Make up Test 3...

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Version 095 – Make up Test 3 – laude – (50995) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 6.0 points You set up a bomb calorimetry experi- ment using 1 liter of water as your heat sink and combusting a 4.409 g sample of propane (C 3 H 8 ). If the initial and final tempera- ture are 24 . 90 C and 77 . 96 C respectively, what is the molar enthalpy of combustion of ethene? (Assume the calorimeter itself ab- sorbs no heat. Assume the density of water is 1 g · mL) 1. - 222 . 0 kJ · mol 1 2. - 22 , 200 kJ · mol 1 3. - 22 . 20 kJ · mol 1 4. - 2 , 220 kJ · mol 1 correct 5. - 222 , 000 kJ · mol 1 Explanation: Δ T = T f - T i = 77 . 96 C - 24 . 90 C = 53 . 06 C = 53 . 06 K m = 1 L · 1000 mL L · 1 . 00 g mL = 1000 g n = 4 . 409 g propane · 1mol 44 . 09 g = 0 . 1 mol propane - Δ H rxn n = Δ H cal n = mc Δ T n = 1000 g · 4 . 184 J g · K · 53 . 06 K 0 . 1 mol = - 2 , 220 kJ · mol 1 002 6.0 points Consider the reaction below: HNO 3 ( ) + H 2 (g) ←→ H 2 O( ) + NO 2 (g) Using the provided table values, calculate Δ G rxn if it is performed under standard con- ditions. Δ H f S species ( kJ mol ) ( J mol · K ) HNO 3 ( ) - 285 . 8 70 NO 2 (g) 33 . 2 240 HNO 3 ( ) - 174 . 1 156 H 2 (g) 0 131 1. 85 kJ · mol 1 2. 6 , 200 kJ · mol 1 3. - 85 kJ · mol 1 correct 4. - 6 , 200 kJ · mol 1 Explanation: Δ H rxn = Σ H f,products - Σ H f,reactants = ( - 285 . 8 kJ · mol 1 + 33 . 2 kJ · mol 1 ) - ( - 174 . 1 kJ · mol 1 )= - 78 . 5 kJ · mol 1 Δ S rxn = Σ S m,products - Σ S m,reactants = (70 J · mol 1 · K 1 + 240 J · mol 1 · K 1 ) - (156 J · mol 1 · K 1 + 131 J · mol 1 · K 1 )= 23 J · mol 1 · K 1 = 0 . 023 kJ · mol 1 · K 1 Δ G rxn = Δ H rxn - T Δ S rxn = - 78 . 5 kJ · mol 1 - (273 K)( - 0 . 023 kJ · mol 1 · K 1 )= - 85 kJ · mol 1 003 6.0 points What is the change in entropy for iodine melting? The standard molar entropy for I 2 (s) and I 2 ( ) are 116 . 14 J · mol 1 · K 1 and 260 . 69 J · mol 1 · K 1 , respectively. 1. 376 . 83 J · mol 1 · K 1 2. - 144 . 55 J · mol 1 · K 1 3. - 376 . 83 J · mol 1 · K 1 4. 144 . 55 J · mol 1 · K 1 correct Explanation: The change in entropy for condensation

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Version 095 – Make up Test 3 – laude – (50995) 2 of water can be described by the equation I 2 (s) ←→ I 2 ( ). Δ S melting = Σ S m,liquid - Σ S m,solid = 260 . 69 J · mol 1 · K 1 - 116 . 14 J · mol 1 · K 1 = 144 . 55 J · mol 1 · K 1 004 6.0 points Ammonia (the common name for NH 3 , the odor of windex and cat urine), has a Δ H vap = 23 . 35 kJ · mol 1 and a S vap = 97 . 43 J · mol 1 · K 1 . What is the normal boiling point of ammonia expressed in centi- grade? 1. 273 C 2. - 0 . 2 C 3. 238 . 7 C 4. - 33 . 3 C correct Explanation: Because boiling is an equilibrium process, Δ G vap = 0 = Δ H vap - T Δ S vap .
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