Chemistry 360 Spring 2015 Dr. Jean M. Standard April 6, 2015 Problem Set 10 Good review problems in Engel & Reid (3rd Ed.): 8.4, 8.5, 8.6, 8.8, 8.9, 8.12, 8.13, 8.15, 8.18, 8.20, 8.25, 8.28, 8.29, 8.33, 8.34, 8.37, 8.43 1. Sketch (roughly to scale) a phase diagram for molecular oxygen given the following information: the triple point occurs at 54.3 K and 1.14 torr; the critical point occurs at 154.6 K and 37828 torr; the normal melting point is 54.75 K; and the normal boiling point is 90.25 K. Does solid molecular oxygen melt under applied pressure? 2. Calculate the melting point of ice under a pressure of 50 bar given that the melting point at 1 bar is 0°C. Assume that the density of ice under these conditions is 0.92 g/mL and the density of liquid water is 1.00 g/mL. The molar enthalpy of fusion of water is 6.01 kJ/mol. 3. If it takes an increase of 1.334 megabars of pressure to change the melting point of a substance from 222°C to 122°C for a change in molar volume of –3.22 cm3/mol, what is the molar enthalpy of fusion of the substance in J/mol? 4. The vapor pressure of liquid benzene obeys the relation ln P = 29.411 − 5893.5 , T where the pressure is in torr and temperature is in Kelvin. Calculate the molar enthalpy of vaporization of benzene and the normal boiling point. € 5. At what pressure does the boiling point of water become 300°C? If oceanic pressure increases by 1 atm for every 10 m, to what ocean depth does this pressure correspond? 6. The sublimation pressures of solid Cl2 are 352 Pa at –112˚C and 35 Pa at –126.5˚C. The vapor pressures of liquid Cl2 are 1590 Pa at –100˚C and 7830 Pa at –80˚C. Calculate the molar enthalpies of sublimation, vaporization, and fusion. 7. Freon-12 (CF2Cl2) was commonly used in spray cans prior to the discovery that it was harmful to the ozone layer. Its enthalpy of vaporization is 20.25 kJ/mol and its normal boiling point is –29.2˚C. Determine the vapor pressure of Freon-12 at 40˚C. 2 8. The vapor pressure of solid uranium hexafluoride, UF6, follows the equation ln P = 29.411 − 5893.5 , T where the pressure is in Pa and temperature is in Kelvin. The vapor pressure of liquid uranium hexafluoride follows the equation € ln P = 22.254 − 3479.9 . T Determine the temperature and pressure of the triple point. € 9. The vapor pressure of liquid mercury is 0.133 bar at 260˚C and 0.533 bar at 330˚C. Assume that the mercury vapor can be treated as an ideal gas and that the enthalpy of vaporization is independent of temperature. Calculate the molar enthalpy and the molar Gibbs free energy of vaporization at 25˚C. 10. Consider the phase diagram of sulfur given below (rhombic and monoclinic are two different solid forms of sulfur). Starting at 298K and 1 atm pressure and considering an increase in the temperature (at constant pressure), comment on the entropy change as the sulfur goes from the rhombic solid phase to the monoclinic sold phase. Is the entropy change expected to be positive or negative? On the basis of the Second Law of Thermodynamics, is the phase transition expected to be spontaneous in an isolated system?