Exam 4-solutions

# Exam 4-solutions - Version 248 – Exam 4 – mccord...

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Unformatted text preview: Version 248 – Exam 4 – mccord – (51600) 1 This print-out should have 25 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. mccord-ch301 10am class only - 51600 C s (water) = 4.184 J/g ◦ C water’s normal boiling pt = 100 ◦ C Thermodynamic Data at 25 ◦ C Δ H ◦ f Δ G ◦ f C p ( kJ mol ) ( kJ mol ) ( J mol K ) H 2 O(l)-285.8-237.2 75.3 CCl 4 (l)-135.4-65.21 131.75 CHF 3 (g)-695.4 51.0 001 4.0 points How is Δ S univ related to Δ G sys ? 1. Δ G sys = T Δ S univ 2. Δ G sys = Δ S univ 3. Δ G sys = Δ S univ T 4. Δ G sys =- Δ S univ 5. Δ G sys =- T Δ S univ correct 6. Δ G sys =- Δ S univ T Explanation: 002 4.0 points Calculate the change in entropy of a large pail of water after 200 J of energy is reversibly transferred to the water at 20 ◦ C. 1.- 200 J · K − 1 2.- 0.733 J · K − 1 3.- 0.683 J · K − 1 4. +0.683 J · K − 1 correct 5. +0.733 J · K − 1 Explanation: T = 20 ◦ C + 273 . 15 = 293 . 15 K Δ S = q T = 200 J 293 . 15 K = +0 . 6822 J K . 003 4.0 points 3.5 g of a hydrocarbon fuel is burned in a ves- sel that contains 250. grams of water initially at 25.00 C. After the combustion, the temper- ature of the water is 26.55 C. How much heat is evolved per gram of fuel burned? 1. 26555 J/g 2. 73.5 J/g 3. 1263 J/g 4. 143 J/g 5. 511 J/g 6. 1764 J/g 7. 463 J/g correct 8. 1105 J/g Explanation: q = m Cp Δ T q = 250 (4.184) 1.55 = 1621.3 J per gram will be 1621.3 J / 3.5 g = 463 J/g 004 4.0 points An endothermic reaction corresponds to one in which 1. change in energy is positive; heat is ab- sorbed. correct 2. change in energy is negative; heat is evolved. Version 248 – Exam 4 – mccord – (51600) 2 3. change in energy is negative; heat is ab- sorbed. 4. change in energy is positive; heat is evolved. Explanation: Endothermic reactions require energy to flow from the surroundings into the system. In other words, heat is absorbed by the sys- tem. Δ H , or the change in energy, is positive for endothermic reactions since the amount of energy in the system increased. 005 0.0 points If more points are awarded on this assign- ment, would you like them added to your score? 1. NO, leave my score alone, I prefer the lower score 2. YES, I would like the points and the higher score. correct Explanation: This should be a no-brainer. Most students want higher scores. If you picked yes, you got credit for the question and you got the extra points you asked for (if they were granted by your instructor). If you answered NO, you also got what you wanted... no points awarded. 006 5.0 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 . 3 kcal....
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Exam 4-solutions - Version 248 – Exam 4 – mccord...

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