Chem 105a Week 6 Practice Problems 1 A system absorbs 196 kJ of heat and the surroundings do 117 kJ of work on the system What is the change in internal energy of the system 2 A 32 5 g iron rod initially at 22 7oC is submerged into an unknown mass of water at 63 2oC in an insulated container The final temperature of the mixture upon reaching thermal equilibrium is 59 5oC What is the mass of the water 3 Mothballs are composed primarily of the hydrocarbon naphthalene C10H8 When 1 025 g of naphthalene burns in a bomb calorimeter the temperature rises from 24 25oC to 32 22oC Find Erxn for the combustion of naphthalene The heat capacity of the calorimeter determined in a separate experiment is 5 11 kJ oC 4 If 50 0 mL of ethanol density 0 789 g mL initially at 7 0oC is mixed with 50 0 mL of water density 1 00 g mL initially at 28 4oC in an insulated beaker and assuming that no heat is lost what is the final temperature of the mixture Cs H2O 4 18 J g oC and Cs ethanol 2 46 J g oC 5 Calculate Hrxn for the reaction CH4 g 4 Cl2 g CCl4 g 4 HCl g Use the following reactions and given H s C s 2 H2 g CH4 g H 74 6 kJ C s 2 Cl2 g CCl4 g H 95 7 kJ H2 g Cl2 g 2 HCl g H 92 3 kJ 6 The explosive nitroglycerin C3H5N3O9 decomposes rapidly upon ignition or sudden impact according to the balanced equation 4 C3H5N3O9 l 12 CO2 g 10 H2O g 6 N2 g O2 g Hrxn 5678 kJ Calculate the standard enthalpy of formation Ho f for nitroglycerin Ho f for CO2 g is 393 5 kJ mol and Ho f for H2O g is 241 8 kJ mol
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