# EXAM 3 - Version 146 – Exam 3 – mccord –(50970 1 This...

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Unformatted text preview: Version 146 – Exam 3 – mccord – (50970) 1 This print-out should have 30 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. McCord CH301 This exam is only for Dr. McCord’s CH301 classes. 001 (part 1 of 2) 10.0 points The following is the plot of vapor pressure vs temperature for three substances, A, B, and C. A B C 100 300 500 700 900 1100- 25 25 50 75 temperature ( ◦ C) pressure(torr) Which, if any, of these substances would be a gas at SATP? 1. C 2. none 3. A and B 4. A and C 5. all 3 are gases 6. A correct 7. B 8. B and C Explanation: Only substance A has a vapor pressure greater than 1 bar (750 torr) at 25 ◦ C. 002 (part 2 of 2) 10.0 points Which ones are gases at STP? 1. all 3 are gases 2. A 3. A and B 4. C 5. none correct 6. B and C 7. A and C 8. B Explanation: At 0 ◦ C all the substances have vapor pres- sures below 760 torr and are therefore liquids. None are gases at STP. 003 10.0 points At any given temperature, how much more quickly will He effuse than Xe? 1. they will diffuse at the same rate 2. 0.12 times more quickly 3. 32.8 times more quickly 4. 5.7 times more quickly correct 5. 8.1 times more quickly 6. .03 times more quickly Explanation: m 1 v 2 1 = m 2 v 2 2 v 1 v 2 = radicalbigg m 2 m 1 = radicalbigg 131 . 3 4 = 5 . 7 004 10.0 points The gauge in this problem is an absolute pres- sure gauge so assume the pressure is exactly Version 146 – Exam 3 – mccord – (50970) 2 as stated in this problem (do not adjust it). An oxygen tank kept at 20 ◦ C contains 28 moles of oxygen and the gauge reads 31 atm. After two weeks, the gauge reads 10 . 5 atm. How much oxygen was used during the two- week period? 1. 7.51 mol 2. 9.25 mol 3. 9.48 mol 4. 18 . 52 mol correct 5. 20.5 mol Explanation: 28 mol- 9 . 48 mol = 18 . 52 mol 005 10.0 points For an ideal gas, pressure and volume are directly proportional. 1. True 2. False correct Explanation: Boyle’s law, V = k 1 P , relates the volume and pressure of a sample of gas at constant temperature. Pressure and volume are in- versely proportional. 006 10.0 points Liquid hydrogen is used as one part of the booster fuel in the space shuttle. What type of forces exist between hydrogen molecules in liquid hydrogen? 1. a mixture of all of these forces 2. dipole forces 3. hydrogen bonding 4. dispersion forces correct Explanation: 007 10.0 points Which of the following gases would you pre- dict to have the largest value of the van der Waals coefficient b ? 1. C 2 FCl 5 correct 2. Cl 2 3. C 2 F 2 Cl 4 4. C 2 F 6 5. CO 2 Explanation: The larger the van der Waals coefficient b , the larger the molecule. The largest molecules have 8 atoms. Of these, C 2 FCl 5 is larger than C 2 F 2 Cl 4 and C 2 F 6 , because Cl is larger than F....
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EXAM 3 - Version 146 – Exam 3 – mccord –(50970 1 This...

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