Lecture notes 2/23
Vapor Pressure and Phase
Diagrams
Ideal gases have no attractive
forces between particles.
Real gases, however, do have
intermolecular forces that affect
how molecules interact. This
can especially be seen as
liquids gain energy to become
gases.
Video clip demonstrating temp
effect on vapor pressure
The vapor pressure of a substance
is a measure of its ability to leave
the liquid phase and become a gas.
When the rate of vaporization is
equal to the rate of condensation
the system is in equilibrium.
Water added to a vacuum
Substances that are volatile
have low intermolecular
attraction, and therefore,
become a gas very easily. They
have higher vapor pressures at
lower temperature.
Boiling occurs when the vapor
pressure of a substance is
equal to the atmospheric
pressure. The normal boiling
point occurs at 1.0 atm.
Temperature is not the only
variable to effect phase changes
of matter. Atmospheric
pressure influences a liquids
ability to become a gas.
Phase diagrams show the
relationship between pressure
and temperature upon the state
of matter for a given substance.
Generic Phase Diagram
Phase boundaries represent the
equilibrium between two phases
of matter. Moving from one
phase across the boundary to
another has some familiar
names and some new names.
Phase Diagram of Water
Looking at the phase diagram of
water it becomes a predictor for
describing the phase of matter
at a given temperature and
pressure.
Phase Diagram of Water
Phase Diagram of CO2
Phase diagram of Iodine