Chm 1316 Honors Freshman Chemistry II
Spring 2001
Exam 3 due 11 AM on 2 April 2001

Work any 5 of the 6 problems! Solutions are here. Email ME questions.
  1. Terminal velocity for a spherical mass falling in the atmosphere is about 120 mph (due to the retarding force of atmospheric friction). But we might as well consider that as zero compared to the initial velocity of an copper meteor of 50,000 m/s. (Copper? You thought meteors were iron, didn't you? And you're right, but I couldn't find liquid iron's properties, and I could find copper's!)

    In the cold of space, the meteor starts out at 200 K. As a solid, it has the average (over the temperature range that takes it all the way to melting) specific heat of 0.44 J/g°C, and an enthalpy of fusion at 1085°C of 210 J/g. As a liquid, it has the average (over the T range from liquid to gas) specific heat of 0.52 J/g°C and an enthalpy of vaporization at 2562°C of 500 J/g.

    1. Find the kinetic energy (in kJ) of 1 kg of Cu travelling 50,000 m/s.
    2. Find the heat required to bring the (1 kg) meteor to its melting point.
    3. Find the heat required to melt it.
    4. Find the heat required to bring the liquid meteor to its boiling point.
    5. Find the heat required to boil it.
    6. Show that (a) exceeds the sum of (b) through (e), proving that meteors ought to vaporize.
    7. But some don't. Big ones. Assuming that they too started at 50,000 m/s, how would you account for their survival to Earth's surface (and hence the dinosaur's demise)?

  2. As a matter of gender pride, you decide to calculate the difference in enthalpies of formation of estrogen (C18H24O2) and testosterone (C19H28O2), but you can't find them in the Handbook of Chemistry and Physics. (I tried.)

    So you hit upon a clever way to work out the problem...choose these steroids as your unknown in the bomb calorimeter experiment. Fortunately, both are solids. That will give you at least their enthalpies of combustion from which you can calculate their enthalpies of formation. Or at least it will after you correct the bomb results to obtain enthalpy.

    1. Balance the combustion reaction of estradiol.
    2. Calculate the correction for the 25°C bomb energy to obtain enthalpy.
    3. Balance the combustion reaction of testosterone.
    4. Calculate it's enthalpy correction at 25°C.
    5. Balance the testosterone ® estradiol reaction in the male brain as if it were an oxidation. [HINT: (a) and (c) make it easy.]
    6. Without even doing the bomb experiments, what can you say about the relative potential (stability of products) of reaction (e) by knowing what the sign of its enthalpy must be?

  3. While Zumdahl's appendix A22 gives DH°f, DG°f, and S° for Na+(aq), it does not list such values for K+(aq). However, it does list them for KOH(aq) by which it means K+(aq) + OH-(aq).

    1. Use the values you can find in Zumdahl's A22 to create a complete listing for K+(aq) including all three thermodynamical values.
    2. How hot would you expect a liter of 1 M KOH(aq) to become having been created by dissolving KOH(s) in initially 25°C water? (CP of water is 1 cal/g°C.)

  4. Consider the reaction 2 NO2(g) ® N2O4(g).
    1. At what temperature would its equilibrium constant KP = 1?
    2. If total pressure were 1 atm, what would be the pressures of each gas at that T ?

  5. Predict and justify the sign of DS°sys for

    1. KOH(s) ® KOH(liq.)
    2. KOH(s) ® KOH(aq)
    3. C2H5OH(liq) + 3 O2(g) ® 2 CO2(g) + 3 H2O(liq)
    4. Mg[H2O]62+ + EDTA4- ® Mg[EDTA]2- + 6 H2O(liq)
    5. NO(g) + O3(g) ® NO2(g) + O2(g)

  6. The following is a table of the log10Kf of gaseous benzene, C6H6(g), as a function of absolute temperature. What is DHf for this molecule at 1000 K? Kf is the equilibrium constant of formation from the elements.

    T (K)90010001100
    log10Kf - 13.945 - 13.574 - 13.184

Comments to Chris Parr Return to CHM 1316 HomePage Last modified 28 March 2001.