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Unformatted text preview: Version 140 hw01a Holcombe (53570) 1 This print-out should have 21 questions. Multiple-choice questions may continue on the next column or page find all choices before answering. 001 10.0 points Which of the following statements is true about an exothermic reaction? 1. The change in enthalpy is positive. 2. We can determine the absolute heat con- tent of the products and reactants. 3. The energy of the products is higher than that of the reactants. 4. Heat is evolved during the reaction. cor- rect Explanation: Exothermic reactions release energy from the system into the surroundings. 002 10.0 points The melting of ice is what kind of process? 1. isotopic 2. enthalpic 3. exothermic 4. endothermic correct Explanation: For H 2 O to go from a solid to a liquid state, energy must be added, which is endothermic. 003 10.0 points Which of the following is true of a general thermodynamic state function? 1. The value of the state function remains constant. 2. The value of a state function does NOT change with a change in temperature of a process. 3. The change in the value of the state func- tion is always positive for endothermic pro- cesses. 4. The change of the value of a state func- tion is independent of the path of a process. correct 5. The change in the value of a state func- tion is always negative for a spontaneous re- action. Explanation: A change in a state function describes a difference between the two states. It is inde- pendent of the process or pathway by which the change occurs. 004 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.- 2458.4 kJ/mol rxn correct 2. 3344.9 kJ/mol rxn 3.- 2233.6 kJ/mol rxn 4.- 3851.9 kJ/mol rxn 5. 1952.1 kJ/mol rxn 6.- 3344.9 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 Version 140 hw01a Holcombe (53570) 2 = 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 005 10.0 points A calorimeter 1. is an indicator of spontaneity....
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- Spring '07