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EXAM 1 - Version 152 Exam 1 sutclie(51045 This print-out...

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Version 152 – Exam 1 – sutcliffe – (51045) 1 This print-out should have 26 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. 001 10.0points Rank the following compounds by mo- lar entropy, from least to greatest: O 2 ( ) , O 2 (g) , O 3 (g) , O 2 (s). 1. O 3 (g) < O 2 ( ) < O 2 (s) < O 2 (g) 2. O 2 (g) < O 2 ( ) < O 2 (s) < O 3 (g) 3. O 3 (g) < O 2 (s) < O 2 ( ) < O 2 (g) 4. O 2 (s) < O 2 ( ) < O 3 (g) < O 2 (g) 5. O 2 (s) < O 2 ( ) < O 2 (g) < O 3 (g) correct Explanation: The three phases of O 2 can be easily ranked, since phase changes have very predictable ef- fects on molar entropy, typically increasing significantly going from solid to liquid and again from liquid to gas. Comparing O 2 (g) to O 3 (g), simply require comparing number of bonds, with O 3 (g) having greater molar entropy because it has more bonds. 002 10.0points Consider the reaction 2 Fe 2 O 3 (s) + 3 C(s) 4 Fe(s) + 3 CO 2 (g) Δ H = 462 kJ / mol Δ S = 558 J / molK Calculate the equilibrium constant for this reaction at 525 C. 1. 1 . 51 × 10 17 2. 1 . 23 × 10 1 3. 8 . 15 × 10 2 correct 4. 1 . 9 × 10 6 5. 3 . 04 × 10 3 6. 2 . 18 × 10 2 Explanation: Δ G = 462000 - (798 . 15 K) (558) = +16632 . 3 J K = e Δ G/ ( RT ) = e 2 . 5064 = 8 . 1558 × 10 2 003 10.0points If the reaction quotient Q for some hypothet- ical reaction is 100, how does Δ G compare to Δ G 0 ? 1. Δ G< Δ G 0 2. There is insufficient information given to determine the answer. 3. Δ G = Δ G 0 4. Δ G> Δ G 0 correct Explanation: Δ G = Δ G 0 + RT ln Q If Q = 100, then the natural log term will be positive. This means that the non standard value of Δ G will be bigger (more positive) than the value of Δ G 0 . 004 10.0points Assuming all of the following salts dissolve completely in water, which one would be the best to use if you were trying to raise the boiling point of the solution? 1. Al 2 (SO 4 ) 3 correct 2. KNO 3 3. NaCl 4. (NH 4 ) 2 Cr 2 O 7 5. Na 3 PO 4 Explanation:
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Version 152 – Exam 1 – sutcliffe – (51045) 2 Al 2 (SO 4 ) 3 is highly soluble and produces 5 ions upon dissolving, has the largest van’t hoff coefficient and is the best choice for at- tempting raise a solution’s boiling point. 005 10.0points Calculate Δ G at 298 K for the reaction C 2 H 5 OH( ) C 2 H 5 OH(g , 0 . 0263 bar) given Δ G = 6 . 2 kJ at 298 K. 1. - 15 kJ 2. 15 kJ 3. 6.2 kJ 4. - 2 . 8 kJ correct 5. 2.8 kJ Explanation: 006 10.0points The osmotic pressure of 1.00 g of a polymer dissolved in benzene to give 200 mL of solu- tion is 1.50 kPa at 25 C. Estimate the average molar mass of the polymer. The gas law con- stant is 0.0821 L · atm · mol 1 · K 1 . 1. 693 g · mol 1 2. 1650 g · mol 1 3. 8260 g · mol 1 correct 4. 41,300 g · mol 1 5. 62,000 g · mol 1 Explanation: 007 10.0points When a liquid boils, which of the following statements is true?
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