Intermolecular forces, heating curves, phase diagrams,Clausius-Clapyron equation, and Unit cell calculations
1.    If 42.0 kJ of heatis added to a 32.0 g sample of liquid methane under 1 atm ofpressure at a temperature of -170 oC, what are the finalstate and temperature of the methane once the system equilibrates?Assume no heat is lost to the surroundings. The normal boilingpoint of methane is -161.5 oC. The specific heats ofliquid and gaseous methane are 3.48 and 2.22 J/g-K,respectively.
2.    The phase diagramfor a hypothetical substance is shown below:
               a) Estimate the normal boiling point and freezingpoint of the substance.
               b) What is the physical state of the substanceunder the following conditions?
                  i) T = 150 K, P = 0.2 atm
                   ii) T = 100 K, P = 0.8 atm
                   iii) T = 300 K, P = 1.0 atm
               c) What is the triple point of the substance?
3.    Benzoic acid,C6H5COOH, melts at 122 oC. Thedensity in the liquid state at 130 oC is 1.08g/cm3. The density of solid benzoic acid at 15oC is 1.266 g/cm3.
               a) In which of these two states is the averagedistance between molecules greater?
               b) Explain the difference in densities at the twotemperatures in terms of the relative kinetic                         energies of themolecules.
4.    At standardtemperature and pressure the molar volume of Cl2 andNH3 gases are 22.06 L and 22.40 L, respectively.
               a) Given the different molecular weights, dipolemoments, and molecular shapes, why are their                                      molar volumes nearly the same?
               b) On cooling to 160 K, both substances formcrystalline solids. Do you expect the molar                                                   volumes to decrease or increase oncooling to 160 K?
               c) The densities of crystalline Cl2 andNH3 at 160 K are 2.02 and 0.84 g/cm3,respectively.                                                     Calculate their molar volumes.
               d) Are the molar volumes in the solid state assimilar as they are in the gaseous state? Explain.e) Would you expect the molar volumes in theliquid state to be closer to those in the solid or                                  gaseous state?
5.    Draw a heating curvefor the conversion of 100 g of ice at -25 oC to steam at125 oC. Temperatures should be labled but the sketchdoes not have to be to scal and the values for q do not need to beidentified.
               a) Comparing the heating of water to the heatingof steam, these lines should have a different                                     slope. Explain why that is.
               b) The length of the line for the conversion ofwater to steam should be much longer than the                                    line representing the amount of heatrequired to convert ice to water. Explain why that is.
               c) The specific heat capacities for ice, water,and steam are 2.03, 4.18, and 2.01 J/g-oC.
                   The DHvap of water is40.65 kJ/mol and the DHfus of water is 6.01kJ/mol.
                   Calculate the amount of heat required toconvert 100 g of ice at 0 oC to steam at 100o.
6. The following quote about ammonia(NH3) is from a textbook of inorganic chemistry: �It isestimated that 26% of the hydrogen bonding in NH3 breaksdown on melting, 7% on warming from the melting to the boilingpoint, and the final 67% on transfer to the gas phase at theboiling point.� From the standpoint of the kinetic energy of themolecules, explain
               a) why there is a decrease of hydrogen-bondingenergy on melting and
               b) why most of the loss in hydrogen bonding
7. Name the phase transition in each of thefollowing situations and indicate whether it is exothermic orendothermic:
               a) Bromine vapor turns to bromine liquid as it iscooled.
               b) Crystals of iodine disappear from anevaporating dish as they stand in a fume hood.
               c) Rubbing alcohol in an open container slowlydisappears.
               d) Molten lava from a volcano turns into solidrock.
8. Compounds like CCl2F2are known as chlorofluorocarbons, or CFC's. These compounds wereonce widely used as refrigerants but are now being replaced bycompounds that are believed to be less harmful to the environment.The heat of vaporization of CCl2F2 is 289J/g. What mass of this substance must evaporate to freeze 200 g ofwater initially at 15 oC? (The heat of fusion of wateris 334 J/g; the specific heat of water is 4.184J/g-oC.)
9. The critical temperatures (K) and pressures(atm) of a series of halogenated methanes are as follows:
               a) List the intermolecular forces that occur foreach compound.
               b) Predict the order of increasing intermolecularattraction, from least to most, for this series of                                   compounds.
               c) Predict the critical temperature and pressurefor CCl4 based on the trends in this table.
10. Explain how each of the following affectsthe vapor pressure of a liquid:
               a) volume of the liquid,
               b) surface area,
               c) intermolecular attractive forces,
               d) temperature,
               e) density of the liquid.
11. Explain the following observations:
               a) Water evaporates more quickly on a hot, dry daythan on a hot, humid day.
               b) It takes longer to cook an egg in boiling waterat high altitudes than it does at lower altitudes.
12. Â Â Â Â Â Â Â a) What is the significance of the critical pointin a phase diagram?
               b) Why does the line that separates the gas andliquid phases end at the critical point?
13. The normal boiling point of acetone, animportant laboratory and industrial solvent, is 56.2 oCand its DHvap is 25.5 kJ/mol. At whattemperature (in oC) does acetone have a vapor pressureof 375 torr?
14. Selenium tetrafluoride, SeF4, isa colorless liquid. It has a vapor pressure of 757 mmHg at 105oC and 522 mmHg at 95 oC. What is its heat ofvaporization in kJ/mol?
15. Iron has a body-centered unit cell with acell dimension of 286.65 pm.
           a) How many iron atoms are in each unit cell?
           b) Calculate the density of iron in g/cm3. (1pm = 10-12 m)
16. Aluminum metal crystallizes in a cubicclose-packed structure (face-centered cubic cell).
           a) How many aluminum atoms are in each unit cell?
           b) Estimate the edge of the unit cell from the atomicradius of Aluminum
                   (1.43 �, 1 � = 10-10 m).
           c) Calculate the density of aluminum metal.
