Conceptual Problems (each problem is worth 6 points – 3 points for the answer and 3 points for the reasoning). You must give a brief explanation of your answer for full credit (a sentence or an appropriate mathematical expression).

  1. An exothermic reaction is run inside a closed, adiabatic vessel with a fixed volume. Is the change in the internal energy positive, negative or zero? Why? Assume that only PV work is possible.

    2. Answer
  2. Will the internal energy increase, decrease or stay the same during the compression of an adiabatic ideal gas system? Why?

    3. Answer
  3. Will the temperature of the freon (the coolant) in your refrigerator increase, decrease or stay the same when it is compressed by the compressor during the cooling cycle? Explain in terms of the Joule Thompson coefficient.

    4. Answer
  4. If I warm an open flask at constant pressure, does the density of the air increase, decrease or stay the same? Why?

    5. Answer
  5. 100 J of PV work is done isothermally on an ideal gas. How much heat is transferred to or from the bath during this process and in which direction?

    6. Answer

    Numerical Problems (each problem is worth 15 points)
  6. A liter of water at constant pressure and 50 C is heated to 100 C and then evaporated by boiling at that temperature. What is the total enthalpy change for this process? The molar heat capacity at constant pressure for water is 75.3 J/(K mole), the molar enthalpy of vaporization at 100 C is 40.66 kJ/mole, then density of water is 1.00 g/ml and the molecular weight of water is 18.

    7. Answer

  7. The isothermal compressibility of copper at 20 C is 0.735 x 10-6 atm-1 and its thermal expansion coefficient is 0.501 x 10-4 K-1. If I were to warm a block of copper from 10 C to 20 C and then compress it back to its original volume by applying pressure, how much pressure would be required? Assume that the thermal expansion coefficient is constant over that temperature range and that the subsequent compression occurs isothermally.                                                Answer
  8. 0.818 moles of an ideal gas at 25 C in a 2 liter container is expanded adiabatically to a final volume of 8 liters. The external pressure is constant at 1 atm. The molar heat capacity at constant volume is 12.47 J/(K mol). Determine q, w, DU, DT, and DH. Express all energies in Joules.   Answer

Applied Problem (25 points)

9) A guy I knew in graduate school used to take an empty 30 ml plastic container, put about 5 grams of dry ice (solid carbon dioxide) in it, seal the cap on it, and place it under the chair of an unsuspecting colleague. Several minutes later, the cap of the container would fly off with a loud pop. For the questions below, you can assume that carbon dioxide gas is ideal and that the amount of air originally in the container before the dry ice was added was negligible. The molecular weight of carbon dioxide is 44.

  1. What would be the pressure in the sealed container after all of the carbon dioxide had sublimated (vaporized to a gas) and come to 25 C?
  2. Assuming that the cap flies off just as the container reaches the pressure calculated in part a, how much work (in Joules) will be done on the surroundings by the subsequent expansion of the gas? Consider the final state to be when the gas has expanded completely and achieved the same temperature and pressure as the surrounding air (25 C and 1 atm). Assume the cap has no mass and no work is involved in popping it off.

Answer