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Unformatted text preview: Exam 3 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. 001 4.0 points At any given temperature, how much more quickly will H 2 diffuse than N 2 ? 1. they will diffuse at the same rate 2. .07 times more quickly 3. 3.7 times more quickly 4. 14 times more quickly 5. 0.3 times more quickly Explanation: m 1 v 2 1 = m 2 v 2 2 v 1 v 2 = radicalbigg m 2 m 1 = radicalbigg 28 2 = 3 . 7 002 4.0 points Real gases behave most nearly like ideal gases at 1. high temperatures and low pressures. 2. low temperatures and low pressures. 3. high temperatures and high pressures. 4. low temperatures and high pressures. 5. high pressures and low molar masses. Explanation: At high temperatures the gas molecules are moving more rapidly and the effects of the attractive forces are less significant. At low pressures the molecules are on average much further apart and the effects of the attractive forces are less significant because there are fewer close encounters. 003 (part 1 of 2) 4.0 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- 50- 25 25 50 temperature ( C) pressure(torr) Which, if any, of these substances would be a gas at SATP? 1. A and C 2. A and B 3. A 4. B and C 5. none 6. B 7. all 3 are gases 8. C Explanation: Both A and B have vapor pressures greater than 1 bar (750 torr) at 25 C and would there- fore be gases. 004 (part 2 of 2) 4.0 points Which substances would be gases at STP? 1. B and C 2. C 3. none 4. A-`i`i`iiv 6v**,3-` /iiVi]\ ViVV Exam 3 mccord (51600) 2 5. all 3 are gases 6. A and C 7. B 8. A and B Explanation: At 0 C only A has a vapor pressure above 760 torr and is therefore a gas at 0 C. B and C will be liquids at STP because their vapor pressures are below 760 torr at 0 C. 005 5.0 points Nitric acid is produced commercially by the Ostwald process. In the first step, ammonia is oxidized to nitric oxide: 4NH 3 (g) + 5O 2 (g) 4NO(g) + 6H 2 O(g) Assume this reaction is carried out in the apparatus diagramed below. 2.00 L NH 3 0.500 atm 1.00 L O 2 1.50 atm The stopcock between the two reaction con- tainers is opened, and the reaction proceeds using proper catalysts. Calculate the partial pressure of H 2 O after the reaction is com- plete. Assume 100% yield for the reaction, assume the final container volume is 3.00 L, and assume the temperature is constant....
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- Spring '07