Problems

Author: John Hutchinson

Problem 1	In the phase diagram for water in figure 6, start at the point where the temperature is 60°C and the pressure is 400 torr. Slowly increase the temperature with constant pressure until the temperature is 100°C. State what happens physically to the water during this heating process.
Problem 2	In the phase diagram for water in figure 6, start at the point where the temperature is 60°C and the pressure is 400 torr. Slowly lower the pressure at constant temperature until the pressure is 80 torr. State what happens physically to the water during this process.
Problem 3	Explain why figure 6 is both a graph of the boiling point of liquid water as a function of applied pressure and a graph of the vapor pressure of liquid water as a function of temperature.
Problem 4	We observe that, when the applied pressure is less than the vapor pressure of a liquid, all of the liquid will spontaneously evaporate. In terms of dynamic equilibrium, explain why no liquid can be present under these conditions.
Problem 5	Using arguments from the Kinetic Molecular Theory and the concept of dynamic equilibrium, explain why, at a given applied pressure, there can be one and only one temperature, the boiling point, at which a specific liquid and its vapor can be in equilibrium.
Problem 6	Using dynamic equilibrium arguments, explain why the vapor pressure of a liquid is independent of the amount of liquid present.
Problem 7	Using dynamic equilibrium arguments, explain why the vapor pressure of a liquid is independent of the volume available for the vapor above the liquid.
Problem 8	Using dynamic equilibrium arguments, explain why a substance with weaker intermolecular forces has a greater vapor pressure than one with stronger intermolecular forces.
Problem 9	According to figure 5 the vapor pressure of phenol is much less than the vapor pressure of dimethyl ether. Which of these substances has the greater intermolecular attractions? Which substance has the higher boiling point? Explain the difference in the intermolecular attractions in terms of molecular structure.
Problem 10	The text describes dynamic equilibrium between a liquid and its vapor at the boiling point. Describe the dynamic equilibrium between a liquid and its solid at the melting point. Using this description, explain why the melting point of a solid varies very little as the pressure increases.