Chapter 11: Intermolecular Forces, Liquids, and Solids.
- What type(s) of IMF is (are) common to
- Xe and methanol (CH3OH)
- CH3OH and acetonitrile (CH3CN)
- NH3 and HF
- Describe the IMF that must be overcome to convert each of the following from a liquid to a gas:
- Which member of the following pairs has the larger London dispersion forces? Explain your choice.
- H2O or H2S
- CO2 or CO
- CH4 or SiH4
- Butane and 2-methylpropane are both nonpolar and have the same molecular formula.
Which molecule would have the higher boiling point, and why?
- What molecular features must a molecule have to participate in hydrogen bonding with other molecules of the same kind?
Which of the following molecules can form hydrogen bonds with other molecules of the same kind?
- Rationalize the difference in boiling points between the members of the following pairs of substances:
- HF (20oC) and HCl (-85oC)
- CHCl3(61oC) and CHBr3 (150oC)
- Br2 (59oC) and ICl (97oC)
Viscosity and Surface Tension
- Why do surface tension and viscosity decrease with increasing temperature?
- Why do substances with high surface tensions also tend to have high viscosities?
- Explain the following observations:
- The surface tension of CHBr3 is greater than that of CHCl3
- As temperature increases, oil flows faster through a narrow tube.
- Raindrops that collect on a waxed automobile hood take on a nearly spherical shape.
Changes of State
- Name the phase transition in each of the following situations, and indicate whether it is exothermic or endothermic
- When water is cooled, it turns to ice.
- Wet clothes dry on a warm summer day.
- Frost appears on a window on a cold winter day.
- Explain why the heat of fusion of any substance is generally lower than its heat of vaporization.
- For many years drinking water has been cooled in hot climates by evaporating it from the surfaces of canvas bags or porous clay pots. How many grams of water can be cooled from 35oC to 22oC by the evaporation of 50 g water? (The heat of vaporization of water in this temperature range is 2.4 kJ/gram. The specific heat of water is 4.18 Joule/gram-Kelvin.
- Ethanol (C2H5OH) melts at -114oC and boils at 78oC. The enthalpy of fusion of ethanol is 5.02 kJ/mol, and its enthalpy of vaporization is 38.56 kJ/mol. The specific heats of solid and liquid ethanol are 0.97 J/g-K and 2.3 J/g-K, respectively. How much heat is required to convert 75.0 g of ethanol at -120oC to the vapor phase at 78oC?
- What is the significance of the critical pressure of a substance?
What happens to the critical temperature of a series of compounds as the force of attractin between molecules increases?
Vapor Pressure and Boiling Point
- Explain how each of the following affects the vapor pressure of a liquid.
- Volume of the liquid
- Surface area
- Intermolecular attractive forces
- Place the following substances in order of increasing volatility. Explain your answer.
CH4, CBr4, CH2Cl2, CH3Cl, CHBr3, and CH2Br2
How do the boiling points vary throughout the series?
- Two pans of water are on different burners of a stove. One pan of water is boiling vigorously, while the other is boiling gently. What can be said about the temperature of the water in the two pans?
- A large container of water and a small one are at the same temperature. What can be said about the relative vapor pressures of the water in the two containers?
- Use the vapor-pressure curve below to estimate the boiling point of diethyl ether at 400 torr.
- Use the vapor-pressure curve above to estimate the external pressure under which ethyl alcohol will boil at 70oC.
- What is the significance of the critical point in a phase diagram?
- Why does the line that separates the gas and liquid phases end at the critical point?
- Refer to the figure below and describe all the phase changes that would occur in each of the following cases:
- Water vapor originally at 0.001 atm and -10oC is slowly compressed at constant temperature until the final pressure is 10 atm.
- Water originally at 100.0oC and 0.50 atm is cooled at constant pressure until the temperature is -10oC.
- The normal melting and boiling points of xenon are -112oC and -107oC, respectively. Its triple point is at -121oC and 282 torr, and its critical point is at 16.6oC and 57.6 atm.
- Sketch the phase diagram for Xe, showing the four points given and indicating the area in which each phase is stable.
- Which is denser, Xe(s) or Xe(l)? Explain.
- If Xe gas is cooled under an external pressure of 100 torr, will it undergo condensation or deposition? Explain.