77.The standard enthalpy of formation of H2O(l) at 298 Kis 285.8 kJ/mol. Calculate the change in internal energyfor the following process at 298 K and 1 atm:H2O(l)88nH2(g)12O2(g)E? 78. A piece of chocolate cake contains about 400 Calories. A nutritional Calorie is equal to 1000 calories (thermochem- ical calories). How many 8-in-high steps must a 180-lb man climb to expend the 400 Cal from the piece of cake? See Exercise 15 for the formula for potential energy. 79.In a bomb calorimeter the bomb is surrounded by waterthat must be added for each experiment. Since the amountof water is not constant from experiment to experiment,mass must be measured in each case. The heat capacityof the calorimeter is broken down into two parts: the water and the calorimeter components. If a calorimetercontains 1.00 kg of water and has a total heat capacityof 10.84 kJ/ C, what is the heat capacity of the calorime-ter components? 80. The bomb calorimeter in Exercise 79 is filled with 987 g of water. The initial temperature of the calorimeter con- tents is 23.32 C. A 1.056-g sample of benzoic acid ( E comb 26.42 kJ/g) is combusted in the calorimeter. What is the final temperature of the calorimeter contents? 81. When 1.00 L of 2.00 M Na 2 SO 4 solution at 30.0 C is added to 2.00 L of 0.750 M Ba(NO 3 ) 2 solution at 30.0 C in a calorimeter, a white solid (BaSO 4 ) forms. The tem- perature of the mixture increases to 42.0 C. Assuming that the specific heat capacity of the solution is 6.37 J C 1 g 1 and that the density of the final solution is 2.00 g/mL, calculate the enthalpy change per mole of BaSO 4 formed. 82.If a student performs an endothermic reaction in a calorime-ter, how does the calculated value of Hdiffer from theactual value if the heat exchanged with the calorimeter isnot taken into account? 83.The enthalpy of neutralization for the reaction of a strongacid with a strong base is 56 kJ/mol of water produced.How much energy will be released when 200.0 mL of0.400 MHCl is mixed with 150.0 mL of 0.500 MNaOH? 84. Three gas-phase reactions were run in a constant-pressure piston apparatus as illustrated. For each reaction, give the balanced reaction and predict the sign of w (the work done) for the reaction. If just the balanced reactions were given, how could you predict the sign of w for a reaction? 85. Consider the following changes: a. N 2 ( g ) N 2 ( l ) b. CO( g ) H 2 O( g ) H 2 ( g ) CO 2 ( g ) c. Ca 3 P 2 ( s ) 6H 2 O( l ) 3Ca(OH) 2 ( s ) 2PH 3 ( g ) d. 2CH 3 OH( l ) 3O 2 ( g ) 2CO 2 ( g ) 4H 2 O( l ) e. I 2 ( s ) I 2 ( g ) At constant temperature and pressure, in which of these changes is work done by the system on the surroundings? By the surroundings on the system? In which of them is no work done? 86. High-quality audio amplifiers generate large amounts of heat. To dissipate the heat and prevent damage to the elec- tronic devices, manufacturers use heat-radiating metal fins.
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