DP’s Study Guide for Chapter 11.
General Chemistry, 4th Ed.”, Hill, Petrucci, McCreary, and Perry (ISBN 0-13-140313-3)
In Chapter 11 we study phase changes and how intermolecular forces are part of that
1.1 Kinetic Molecular Theory of Gases is extended to the liquid and solid phase.
molecules in a liquid are closer together than a gas and are attracted to each other by
intermolecular forces the magnitude of which depends upon the molecule.
In solids the
molecules are closer still moving much less.
To go from one phase to another an energy
change is needed.
Most folks associate phase changes with temperature.
This is true, but
a limited view of what really goes on because we only operate at a single pressure. This
“phase change” energy is required no matter what the temperature, and is roughly
independent of temperature.
Some Enthalpies of Vaporization at 298 K are listed in
At 0 C
, solid water (aka ice), liquid water, and water vapor (do not say
steam) can all exist together
Learn: the terms melting (fusion), freezing, vaporization, condensation, sublimation, and
Be able to work problems associated with each change:
Problems: 17, 21, 32, 37.
If you are changing the temperature of a single phase, solid, liquid, or gas, the
energy needed is determined by the heat capacity of the stuff in that particular phase.
Chapter 6.5 where you can get the rink dink formula ∆H = ms∆T.
In this chapter
energies need to change phase and temperature are considered together.
transitions are diagramed in heating or cooling curves.
11.2 Vaporization and Vapor pressure.
Molecules in a liquid are not stationary but move around.
According to the KMT, some
of these molecules have enough energy to escape the liquid, ie defeating the
After escaping the molecules of liquid strike the air above this
produces something called vapor pressure.
Some of the molecules leave the area of the
liquid completely others loose enough energy and return to the liquid.
This leaving and
returning process is called dynamic equilibrium, molecules enter and leave the liquid at
the same rate giving the appearance that nothing is going on.
A version of the idea gas
law equation can be used to calculate vapor pressures and vapor volumes:
Problems 27, 29, 31,
As the temperature rises the average KE of the molecules increases and more leave the
liquid increasing vapor pressure vapor pressure increases with temperature.
temperature at which the vapor pressure of the liquid equals the pressure of gas over the
liquid is called the boiling point.
Of course if you take some of the air over the liquid
away, the liquid will boil at a lower temperature.
Conversely, if air pressure is added, the