Exam 4-solutions - Version 036 Exam 4 sutcliffe(90830 This...

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Version 036 – Exam 4 – sutcli ff e – (90830) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0 points The correct name for HBrO 3 (aq) is 1. bromic acid. correct 2. perbromic acid. 3. hydrobromic acid. 4. bromous acid. Explanation: HBrO 3 is brom ic acid. Brom ous acid has one fewer oxygen atom than the “-ic” acid HBrO 2 . Per brom ic acid has one more oxygen atom than the “-ic” acid and has the formula HBrO 4 . Hydro bromic acid is an aqueous so- lution of hydrogen bromide (HBr). 002 10.0 points A system did 150 kJ of work and its internal energy increased by 60 kJ. How much energy did the system gain or lose as heat? 1. The system gained 210 kJ of energy as heat. correct 2. The system lost 210 kJ of energy as heat. 3. The system gained 90 kJ of energy as heat. 4. The system lost 90 kJ of energy as heat. 5. The system gained 60 kJ of energy as heat. Explanation: 003 10.0 points Using the provided bond energy data, calcu- late the change in enthalpy for the reaction below. 6 HCl(g) + N 2 (g) -→ 2 NH 3 (g) + 3 Cl 2 (g) Bond Energy H - Cl 432 kJ · mol - 1 N N 945 kJ · mol - 1 N - H 391 kJ · mol - 1 Cl - Cl 199 kJ · mol - 1 1. 787 kJ · mol - 1 2. - 594 kJ · mol - 1 3. - 2 , 357 kJ · mol - 1 4. 594 kJ · mol - 1 correct 5. 2 , 357 kJ · mol - 1 Explanation: Δ H = BE reactants - BE products = 6(432 kJ · mol - 1 ) + 945 kJ · mol - 1 - 6(391 kJ · mol - 1 ) + 3(199 kJ · mol - 1 ) = 594 kJ · mol - 1 004 10.0 points Methane has a heat of combustion of about 50 kJ/g. About how much heat would be produced if 15 moles of methane were burned? 1. over 15,000 kJ 2. 750 kJ 3. 12,000 kJ correct 4. 9,600 kJ 5. 800 kJ Explanation: Δ H comb = 50 kJ/g n = 15 mol MW methane = 16 g Molar Δ H comb = ( - 50 kJ / g)(16 g / mol) = 800 kJ / mol . The amount of heat produced from burning 15 moles is (15 mol)(800 kJ / mol) = 12 , 000 kJ .
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Version 036 – Exam 4 – sutcli ff e – (90830) 2 005 10.0 points The fact that a refrigerator requires energy to move heat from a colder object (the in- side of the refrigerator) to a hotter object (the outside of the refrigerator) is a real life observation of which law of thermodynamics? 1. first law 2. second law correct 3. third law 4. fourth law Explanation: The Second Law of Thermodynamics says that in spontaneous changes, the universe tends toward a state of greater disorder. Re- frigeration decreases entropy of the system but it requires energy from reactions that in- crease entropy (like burning coal). 006 10.0 points Which statement would be the best interpre- tation of the First Law of Thermodynamics? 1. The total amount of energy in the uni- verse is constant. correct 2. The total amount of entropy in the uni- verse is increasing. 3. The total amount of energy in the uni- verse is increasing. 4. The total amount of matter in the uni- verse is constant. Explanation: The first law is the law of conservation of energy and mass (not matter). The second law deals with entropy.
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