105A_labquiz2_spring06_key

# 105A_labquiz2_spring06_key - Experiment#7 Reaction Enthalpy...

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Experiment #7 – Reaction Enthalpy 1. The specific heat capacity of helium gas (4.003 g/mol) is 5.3 J/g K. The specific heat capacity of hydrogen gas (2.016 g/mol) is 14.3 J/g K. One thousand joules of energy is transferred to each of two, one-liter, perfectly adiabatic calorimeters containing one liter of each gas at 1.00 atm and 298K. Which of the following statement is true? a) the calorimeter containing helium gas will reach a higher final temperature. b) the mass of gas in each calorimeter is the same. c) the calorimeter containing hydrogen gas will reach a higher final temperature. d) An adiabatic calorimeter does not change temperature. e) both calorimeters will reach the same final temperature. 2. The reaction of an acid such as HCl with a base such as NaOH in water involves the exothermic reaction HCl(aq) + NaOH(aq) ---> NaCl(aq) + H2O In one experiment, a student placed 50.0 mL of 1.00 M HCl in a coffee-cup calorimeter and carefully measured its temperature to be 20.5 ° C. To this was added 50.0 mL of 1.00 M NaOH solution whose temperature was also 20.5 ° C. The mixture was quickly stirred, and the student noticed that the temperature of the mixture rose to 27.6 ° C. What was the heat of reaction? Ignore the heat capacity of the calorimeter in your calculation. The heat capacity of all solutions is 4.19 J/g K. The density of all solutions is 0.995 g/mL. . a) +59 kJ/mol. b) +30 kJ/mol. c) –118 kJ/mol. d) –30 kJ/mol. e) –59 kJ/mol. ONLY THE SCANTRON SHEET WILL BE GRADED 1

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Experiment #8 – Molar Volume 3. Sulfur Hexafluoride is used as a gaseous dielectric in high voltage switches, circuit breakers and other electrical equipment. It is expected to behave non-ideally as evidenced by its very large van der Walls “a” and “b constant values. The molar volume of sulfur hexafluoride was determined using the method of Experiment #8. The following data was collected. Mass of flask with air = 225.765 g Mass of water occupying the gaseous volume of the flask = 123.345 g Mass of flask filled with SF 6 = 226.392 g Determine the experimentally measured molar volume of SF 6 gas at one atm and 298 K from this measurement. R = 8.314 J/mol K = 0.08206 L atm/ mol K Density of air = 1.622 g/L Atomic mass SF 6 = 146.07 Density of water = 1.099 g/mL Your experimental measurement contains error. Simply using the ideal gas law to calculate V/n = RT/P will result in the wrong answer. a) 10.1 L.
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## This note was uploaded on 02/27/2008 for the course CHEM 105ALg taught by Professor Bau during the Spring '07 term at USC.

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105A_labquiz2_spring06_key - Experiment#7 Reaction Enthalpy...

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