full_solutions_MT1_B_2006 - 2R03 Midterm 1B Fri Oct 13, '06...

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2R03 Midterm 1B – Fri Oct 13, ’06 - SOLUTIONS (1) This is version A. Please mark circle A for exercise 1 of the scantron sheet. (2) Assume that you define your thermodynamical system as a non-adiabatic cylinder containing the liquid ethanol (CH 3 -CH 2 -OH (l) ) covered by a mobile piston. Imagine that you then start the exothermic combustion of ethanol. Which of the following statements is true: a. During the combustion of ethanol work will be done by the system on the surroundings. b. During the combustion of ethanol work will be done by the surroundings on the system. c. The U associated with the combustion of ethanol is the same as the heat transferred to the surroundings. d. The U associated with the combustion of ethanol is the same as the work done during the combustion. Solution: The combustion reaction for ethanol is: CH 3 -CH 2 -OH (l) + 3 O 2(g) 2 CO 2(g) + 3 H 2 O (l) So the total number of gas moles decreases as a result of this combustion the surroundings will do work work on the system (b) is true and (a) is false. (c) is also false because it neglects the PV-work. (d) is false because it neglects the heat of combustion transferred to the surroundings. Correct answer is (b) (3) Consider one mole of a gas that at 25 o C occupies a volume of 24.8 L and exerts a pressure of 0.1 bar. Which of the following statements is true: a. The gas behaves ideally b. The gas does not behave ideally due to the presence of attractive intermolecular interactions c. The gas does not behave ideally due to the presence of repulsive intermolecular interactions d. We cannot say whether the gas behaves ideally or non ideally based on the data provided Solution: We know that at P = 1 bar and at T = 298.15K one mole of an ideal gas occupies 24.8 L. The fact that the actual pressure of the gas under investigation is less than 1 bar indicates that it is non ideal due to
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full_solutions_MT1_B_2006 - 2R03 Midterm 1B Fri Oct 13, '06...

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