Exam 1 - Version 211 Exam 1 mccord(50950 This print-out...

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Version 211 – Exam 1 – mccord – (50950) 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 The ideal gas law does not model actual gas behavior in the limit of high pressure because it fails to take into account 1. the kinetic energy of the gas particles. 2. that the particles are smaller at high pres- sure. 3. the distribution of velocities of the gas particles. 4. that the pressure depends on the number of gas particles. 5. the interactions between the gas particles. correct Explanation: The ideal gas law fails at high pressure as the interactions between the gas molecules becomes more important. Kinetic molecular theory arrives at the ideal gas law and it takes into account both the KE and the distribution of velocities. The molecular size does not vary to any significant extent with pressure. The pressure depends on the number of molecules in the ideal gas law. 002 10.0points Which of the following is an intensive prop- erty? 1. number of moles of molecules 2. mass 3. density correct 4. weight 5. volume Explanation: Intensive properties are independent of the amount of matter present. The density of a substance will be the same regardless of the size (large or small) of the sample. 003 10.0points What is the root mean square speed of carbon dioxide molecules at 98 C? 1. 45.6 m · s 1 2. 459 m · s 1 correct 3. 236 m · s 1 4. 574 m · s 1 5. 153 m · s 1 Explanation: T = 98 C + 273 . 15 = 371 . 15 K MW = 44 . 0095 g / mol = 0 . 0440095 kg / mol R = 8 . 314 N K · mol The root mean square speed is v = radicalbigg 3 R T MW = radicalBigg 3 ( 8 . 314 N K · mol ) (371 . 15 K) 0 . 0440095 kg / mol = 458 . 635 m / s . 004 10.0points An ideal gas initially has a volume of 10 L at a temperature of 300K and a pressure of 4 atm. It undergoes a process which results in the temperature being 600 K and the volume being 20 L. What is the final pressure? 1. 4 atm correct 2. 16 atm 3. 1 atm 4. 2 atm 5. 8 atm
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Version 211 – Exam 1 – mccord – (50950) 2 Explanation: The gas doubles in temperature which would result in the pressure doubling. How- ever, the volume also doubles which would reduce the pressure by 2. So the pressure doesn’t change. P 1 V 1 T 1 = P 2 V 2 T 2 P 2 = P 1 V 1 T 2 V 2 T 1 = 4 · 10 · 600 20 · 300 = 4 atm 005 10.0points Consider the following reaction: 2 A (g) + 3 B (g) -→ C (g) + 2 D ( ) If 42 L of gas A is mixed with 45 L of gas B at the same pressure and temperature to give an initial volume of 87 L. After A and B react, the total volume is different, what is it? Assume the reaction runs to completion. 1. 25.0 2. 31.0 3. 21.0 4. 27.0 5. 15.0 6. 13.0 7. 23.0 8. 29.0 9. 19.0 10. 17.0 Correct answer: 27 L. Explanation: Because the pressure and temperature are constant, the problem can be worked in liters (volume units) instead of moles. 45 L of B 2 L of A 3 L of B = 30 L A reacts This will leave behind (excess) A = 42 - 30 = 12 L excess A amount of C made = 45 L B (1/3) = 15 L of C made.
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