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# exam3answers - Gu Phillip – Exam 3 – Due Dec 5 2007...

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Unformatted text preview: Gu, Phillip – Exam 3 – Due: Dec 5 2007, midnight – Inst: Brodbelt 1 This print-out should have 24 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. The due time is Central time. Brodbelt CH301 Exam 3 Fall 2007 Use of programmable calculators or cell phones is considered cheating and thus is pro- hibited. You may not leave the room for any reason. You may not start the exam after 7;15 pm. GOOD LUCK! 001 (part 1 of 1) 10 points Water molecules bind to each other mainly by 1. breaking an O H bond in neighboring water molecules. 2. electrons being paired between them. 3. ejecting electrons from oxygen. 4. oxygen lone pair interactions with hydro- gen atoms of a neighboring molecule. cor- rect Explanation: O · · · · δ + H δ + H δ- ··· δ + H · · ·· O H δ + δ- 002 (part 1 of 1) 10 points Given: 4HCl(g) + O 2 (g) → 2H 2 O( ‘ ) + 2Cl 2 (g) Δ H =- 202 . 4 kJ/mol rxn What is the expected energy change for the reaction of three moles of H 2 O and six moles of Cl 2 ? 1. 303.6 kJ correct 2.-67.5 kJ 3. 67.5 kJ 4. 1821 kJ 5.-303.6 kJ 6.-202.4 kJ 7.-607.2 kJ 8.-1821 kJ 9. 607.2 kJ 10. 202.4 kJ Explanation: The first equation needs to be multiplied by 1 2 in order to get the equation we’re interested in. Thus its Δ H is multiplied by 1 2 as well. The second equation needs to be multiplied by two in order to get the equation we’re interested in. We also multiply its Δ H by two. The third equation needs to be reversed, so the sign of its Δ H should change. Then we add the equations to get the equa- tion we’re interested in. We also add the ad- justed Δ H values to get the answer,- 1015 . 4 kJ/mol rxn. 003 (part 1 of 1) 10 points Propane (C 3 H 8 ) is burned in oxygen to pro- duce carbon dioxide and water. The heat of combustion of propane is -2012 kJ/mole. How much heat is given off when 3.0 mol C 3 H 8 are reacted with 10.0 mol O 2 ? 1. 7392 kJ 2. 4024 kJ correct 3. 2012 kJ 4. 916 kJ 5. 6036 kJ Gu, Phillip – Exam 3 – Due: Dec 5 2007, midnight – Inst: Brodbelt 2 6. 5122 kJ 7. 672 kJ 8. 1555 kJ Explanation: 004 (part 1 of 1) 10 points The molecules in the reaction NH 3 (g) + 3F 2 (g) → NF 3 (g) + 3HF(g) contain only single bonds. What is the heat evolved or absorbed per mole of NH 3 that reacts? These bond energy values might be useful: H-F 566 kJ/mol, F-F 158 kJ/mol, N-H 391 kJ/mol, N-F 272 kJ/mol. 1.- 566 kJ/mol 2.-289 kJ/mol 3. None of these 4.- 867 kJ/mol correct 5.- 1105 kJ/mol 6. +151 kJ/mol 7. +867 kJ/mol 8. +1105 kJ/mol Explanation: 3(391)+3(158)-3(272)-3(566) = -867 005 (part 1 of 1) 10 points Which statement about intermolecular forces in liquids is FALSE?...
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exam3answers - Gu Phillip – Exam 3 – Due Dec 5 2007...

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