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7 - ching(yyc99 Homework 7 Lyon(53750 This print-out should...

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ching (yyc99) – Homework 7 – Lyon – (53750) 1 This print-out should have 52 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points Based on the reaction CH 4 (g) + 2 O 2 (g) CO 2 (g) + 2 H 2 O(g) and its energy profile CH 4 (g) + 2 O 2 (g) (1 mol) (2 mol) Energy difference = - 802.3 kJ (heat released) CO 2 (g) + 2 H 2 O(g) (1 mol) (2 mol) the reaction 1. has a high activation energy. 2. is nonspontaneous. 3. violates the first law of thermodynam- ics. 4. is exothermic. correct Explanation: In an exothermic reaction the energy of the reactants is higher than that of the products; as the reaction proceeds, energy is released. 002 10.0 points The molecules in the reaction NH 3 (g) + 3 F 2 (g) NF 3 (g) + 3 HF(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. +867 kJ/mol 3. None of these 4. +151 kJ/mol 5. -289 kJ/mol 6. - 1105 kJ/mol 7. +1105 kJ/mol 8. - 867 kJ/mol correct Explanation: 3(391)+3(158)-3(272)-3(566) = -867 003 10.0 points Hot coffee in a vacuum flask (thermos) is an example of what type of system? 1. closed 2. open 3. isolated correct Explanation: An isolated system cannot exchange energy nor matter with the surroundings. 004 10.0 points Work done (by/on) the system is negative, and heat (gained/lost) by the system is posi- tive. 1. on, gained 2. by, gained correct 3. by, lost 4. on, lost Explanation: The sign conventions for process functions (like work and heat) are such that a positive sign is attributed to the system if it gains energy (in the form of heat or work).

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ching (yyc99) – Homework 7 – Lyon – (53750) 2 005 10.0 points Carbon monoxide reacts with oxygen to form carbon dioxide by the following reaction: 2 CO(g) + O 2 (g) 2 CO 2 (g) Δ H for this reaction is - 135 . 28 kcal. How much heat would be released if 12.0 moles of carbon monoxide reacted with suffi- cient oxygen to produce carbon dioxide? 1. 405.84 kcal 2. 541.12 kcal 3. 811.68 kcal correct 4. 135.28 kcal 5. 1623.36 kcal 6. 270.56 kcal Explanation: Δ H = - 135 . 28 kcal n CO = 12.0 mol parenleftBig - 135 . 28 kcal 1 mol rxn parenrightBigparenleftBig 1 mol rxn 2 mol CO parenrightBig × (12 mol CO) = - 811 . 68 kcal so 811 . 68 kcal were released. 006 10.0 points Which of the following reactions as written corresponds to a heat of formation reaction? 1. SO 2 (g) + 1 2 O 2 (g) SO 3 (g) 2. CO 2 (s) CO 2 (g) 3. Na(s) + 1 2 Cl 2 (g) NaCl(s) correct 4. 2 H 2 (g) + O 2 (g) 2 H 2 O( ) Explanation: All of the reactants in a formation reaction must be ELEMENTS in their thermochemical standard state. AND, to match table values, only 1 MOLE of product can be formed be- cause standard table values are in kJ/mol. Only the NaCl fits this definition. The H 2 O reaction unfortunately is forming 2 moles of water instead of one. 007 10.0 points What factor determines whether a reaction will be exothermic or endothermic?
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