Exam 3 solution - Version 070 Exam Three Shear Shear(52375...

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Version 070 – Exam Three: Shear – Shear – (52375) 1 This print-out should have 27 questions. Multiple-choice questions may continue on the next column or page – find all choices before answering. DrRuth says: In all cases, select the answer that BEST answers the question asked. The total number of points on this exam is 350. Read the whole thing first and plan which to answer first because you feel confident about them. Notice the harder ones and save them up till last so you don’t use up all your time working on them. Unless otherwise stated, assume the gases in all questions are ideal. Shear 52375 g = 9 . 8 m / s 2 1 atm = 101325 Pa = 760 torr R = 0.08206 L atm K 1 mol 1 R = 0.08314 L bar K 1 mol 1 R = 8.314 J K 1 mol 1 Effusion rate of gas 1 Effusion rate of gas 2 = radicalbigg M 2 M 1 Effusion rate at T 1 Effusion rate at T 2 = radicalbigg T 1 T 2 KE = 2 / 3 RT u rms = radicalbigg 3 RT M 001 10.0 points Which is the weakest type of attractive force between particles? 1. hydrogen bond 2. dispersion forces correct 3. covalent bond 4. ionic bond Explanation: London forces, dispersion forces, or induced dipoles all describe the same intermolecular force. London forces are induced, short-lived, and very weak. Molecules and atoms can experience London forces because they have electron clouds. London forces result from the distortion of the electron cloud of an atom or molecule by the presence of nearby atoms or molecules. Permanent dipole-dipole interactions are stronger than London forces and occur be- tween polar covalent molecules due to charge separation. H-bonds are a special case of very strong dipole-dipole interactions. They only occur when H is bonded to small, highly electro- magnetic atoms – F, O or N only. Ion-ion interactions are the strongest due to extreme charge separation and occur between ionic molecules. They can be thought of as both inter- and intramolecular bonding. 002 10.0 points Which of the following is NOT true about gases? 1. Gases can expand without limit. 2. The density of a gas can be increased by applying increased pressure. 3. Gases exert pressure on their surround- ings. 4. The gas is at STP if it is at 273 K and 1 atm. 5. The volume a gas occupies is directly proportional to its molecular weight. correct Explanation: Volume is directly proportional to number of moles of a gas present, not the molecular weight: P V = n R T V n 003 10.0 points A mixture of CO, CO 2 and O 2 is contained
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Version 070 – Exam Three: Shear – Shear – (52375) 2 within a 275 mL flask at 0 C. If the total pres- sure is 780 torr, the CO has a partial pressure of 330 torr and the CO 2 has a partial pressure of 330 torr, what is the partial pressure of O 2 ? 1. 330 torr 2. 660 torr 3. 120 torr correct 4. 900 torr 5. 780 torr Explanation: P total = 780 torr P CO = 330 torr P CO 2 = 330 torr P total = P CO + P CO 2 + P O 2 P O 2 = P total - P CO - P CO 2 = 780 torr - 330 torr - 330 torr = 120 torr 004 10.0 points To promote ideal behavior of a gas, one should (raise/lower) the pressure and (raise/lower) the temperature of the gas.
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