J. Muench WORKSHEET #6 ______________________ CHEM 161 name 1. Given the following thermochemical reaction: H2(g) + F2(g) 2 HF(g) ; H = 537 kJ What is H for the reaction below? HF(g) ½ H2(g) + ½ F2(g) 2. Solid sodium metal reacts very vigorously with water in a highly exothermic reaction. 2 Na(s) + 2 H2O(l) 2 NaOH(aq) + H2(g) ; H = 368.6kJ a. What amount of heat is produced when 0.500mol of Na(s) completely reacts? b. What amount of heat is produced when 0.875g of Na(s) completely reacts? c. What amount of heat is produced if 2,500mL of H2(g) is collected? Use a density of 0.082g/mL for H2(g) at 25oC. 3. A 237g sample of molybdenum metal is heated to 100.1oC and then dropped into an insulated cup containing 244g of water at 10.0oC. If the final temperature of the water and metal in the cup is 15.3oC, then what is the specific heat of molybdenum?J. Muench 4. Insoluble AgCl precipitates out according to the reaction below. When 250.mL of 0.18M AgNO3 and 125mL of 0.36M NaCl are mixed, the temperature of the solution increases from 21.15oC to 22.90oC. What is the enthalpy ( H) per mole of AgCl formed? Assume the density of the solutions are 1.00g/mL and the specific heat is 4.18 J/goC. The baqlanced reaction is: AgNO3(aq) + NaCl(aq)  AgCl(s) + NaNO3(aq) 5. A 1.800g sample of octane, C8H18, is burned a calorimeter whose total heat capacity is 11.66 kJ/oC. If the temperature of the calorimeter increased from 21.36oC to 28.78oC, then what is the H for the combustion of one gram of octane? How much is it for one mole? 6. Using Hess’s Law, calculate H for the reaction (note – please do not use appendix C) N2(g) + 2 H2(g) N2H4(l) given the following two reactions: (1) N2H4(l) + O2(g) N2(g) + 2 H2O(l) ; H = 622.2kJ (2) H2(g) + ½ O2(g) H2O(l) ; H = 285.8kJJ. Muench 7. Using Hess’s Law, calculate H for the reaction (note – please do not use appendix C) P4O10(s) + 6 PCl5(g) 10 POCl3(g) ; H = ? given the following four reactions: (1) P4(s) + 6 Cl2(g) 4 PCl3(g) ; H = 1,225.6 kJ (2) P4(s) + 5 O2(g) P4O10(s) ; H = 2,967.3 kJ (3) PCl3(g) + Cl2(g) PCl5(g) ; H = 84.2 kJ (4) PCl3(g) + ½ O2(g) POCl3(g) ; H = 285.7 kJ 8. Using appendix C, determine the H for each reaction below. a. Fe2O3(s) + 6HCl(g) 2 FeCl3(s) + 3 H2O(g) b. 4NH3(g) + O2(g) 2N2H4(g) + 2H2O(l) 9. Using both the following reaction (including its Ho value) and Appendix C, determine Hfo for CaC2(s). CaC2(s) + 2 H2O(l) Ca(OH)2(s) + C2H2(g) ; Ho = 127.2kJJ. Muench 10. An 11.0g of CaCl2(s) sample is dissolved in 125.0g of H2O(l) in a coffee cup calorimeter. If the initial temperature of both substances are 25.0oC, then determine the final temperature of the solution. Assume that the specific heat of the solution is 4.184J/goC, the Hfo for Ca+2(aq) is 542.9 kJ/mol (all others are in App. C), and the coffee cup is a perfect insulator. CaCl2(s) Ca+2(aq) +