CH_301-Sutcliffe-Final_Exam

CH_301-Sutcliffe-Final_Exam - Version 225 Final TTh...

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Unformatted text preview: Version 225 Final TTh sutcliffe (50985) 1 This print-out should have 46 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points A drop of liquid tends to have a spherical shape due to the property of 1. viscosity. 2. vapor pressure. 3. capillary action. 4. surface tension. correct 5. close packing. Explanation: Molecules on the surface of a liquid are influenced by intermolecular attractions to- wards the interior; these attractions pull the surface layer toward the center. The most sta- ble situation is one in which the surface area is minimal. For a given volume, a sphere has the least possible surface area. 002 10.0 points Determine the enthalpy change of reaction at 25 C for 4 HNO 3 ( ) + 5 N 2 H 4 ( ) 7 N 2 (g) + 12 H 2 O(g) H f for HNO 3 is 174 . 1 kJ/mol; H f for H 2 O is 241 . 8 kJ/mol; H f for N 2 H 4 is +50 . 63 kJ/mol. 1. 1952.1 kJ/mol rxn 2. 3344.9 kJ/mol rxn 3. 3344.9 kJ/mol rxn 4. 2458.4 kJ/mol rxn correct 5. 3851.9 kJ/mol rxn 6. 2233.6 kJ/mol rxn Explanation: Reactants: H f HNO 3 ( ) = 174 . 1 kJ/mol H f N 2 H 4 (g) = 50 . 63 kJ/mol Products: H f H 2 O(g) = 241 . 8 kJ/mol H f N 2 = 0 H rxn = summationdisplay n H f prod summationdisplay n H f rct = bracketleftbigg 12 parenleftbigg 241 . 8 kJ mol parenrightbiggbracketrightbigg bracketleftbigg 4 parenleftbigg 174 . 1 kJ mol parenrightbigg + 5 parenleftbigg 50 . 63 kJ mol parenrightbiggbracketrightbigg = 2458 . 4 kJ mol rxn 003 10.0 points Diamond and graphite are two crystalline forms of carbon. In which form are the bonds between the C atoms arranged at tetrahedral angles to each other? 1. Neither of these 2. diamond correct 3. graphite Explanation: Graphite forms flat sheets C C C C C C C C C C C C C C while diamond is tetrahedral C C C C C Version 225 Final TTh sutcliffe (50985) 2 in form. 004 10.0 points What is the molarity of 12.5 g CH 3 OH in 50.0 mL of solution? 1. 2.50 M 2. 0.250 M 3. 0.00250 M 4. 7.81 M correct 5. 0.00781 M Explanation: m CH 3 OH = 12.5 g V = 50.0 mL Molarity is moles per liter, so we need to convert the mass into moles and the volume from mL to L. The number of moles are 12 . 5 g parenleftbigg 1 mol 32 . 0 g parenrightbigg = 0 . 391 mol and the volume is 50 . 0 mL parenleftbigg 1 L 1000 mL parenrightbigg = 0 . 0500 L . The molarity is ? M CH 3 OH = . 390 mol CH 3 OH . 0500 L soln = 7 . 81 M CH 3 OH 005 10.0 points How many double bonds are in the compound CH 2 CHCH 2 CHCH 2 ? 1. 3 2. 3. 4 4. 1 5. 2 correct Explanation: The Lewis dot structure is H C H C H C H H C H C H H 006 10.0 points A substance is 35.7% carbon by mass. How much carbon could be recovered from 769 g of the substance?...
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CH_301-Sutcliffe-Final_Exam - Version 225 Final TTh...

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