# Four major points on a phase diagram - PowerPoint

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```							       Phases of matter: Comparison
Property         Solid               Liquid             Gas
Particles        Closely packed      More densely       Most
High density        packed than in     compressible-
(But…Water is       gas                least densely
different!)                            packed

Particle         Vibrate weakly      Can change         Can change
movement         around fixed        positions with     positions with
positions           other particles    other particles
Lowest kinetic                         Highest kinetic
energy                                 energy
Intermolecular   Most effective      Stronger than in   Least effective
forces           (strongest)         gases              (weakest)
Shape and        Both definite       Definite volume    No definite
volume                               only               shape or volume
Mullis                                  1
Surface tension
• Force that pulls adjacent parts of a liquid
surface together.
• The higher the attractive forces between
particles in the liquid, the higher the
surface tension.
• Hydrogen bonds make water have
higher surface tension than most liquids.
Soap

Water droplet
Mullis                   2
Solids
• Crystalline solids: Particles are arranged
in an orderly, geometric, repeating
pattern.
• Examples: Emerald, diamond, calcite
• Amorphous solids: (Without shape)
• Particles are arranged randomly.
• Examples: Glass, plastic

Mullis                 3
Changing states
• Equilibrium: When there is no net
change in a system.
• Dynamic equilibrium:
• When a vapor is in equilibrium with its
liquid as one molecule leaves the liquid to
become a vapor, another molecule leaves
the vapor to become a liquid. In other
words, an equal number of molecules will
be found moving in both directions.
Mullis                     4
LeChâtelier’s Principle
When a system at equilibrium is disturbed
by application of stress, it attains a new
equilibrium position that minimizes the
stress.

 "If stress is applied to a system at
equilibrium,
the system will tend to readjust so that
the stress is reduced."
Mullis                   5
Boiling Point
• Vapor pressure: Pressure exerted by a
vapor = Pressure of the liquid at given
temperature
• Liquid boils when its vapor pressure
equals pressure of the atmosphere.
• Boiling is the conversion of a liquid to vapor
within the liquid as well as at its surface.
• Boiling point is the temperature at which the
equilibrium vapor pressure of the liquid
equals the atmospheric pressure.
• Volatile liquids are liquids that evaporate
Mullis                    6
Boiling Point, cont.
• High elevation: Low atmospheric pressure
• Low atmospheric pressure = lower boiling
point
• High pressure in pressure cooker =
increased boiling point, faster cooking
• If pressure above liquid increases, the
liquid temperature rises until it matches
the new pressure and boils again.

Mullis                7
Separation by Distillation
• Distillation is the separation of liquid
substances according to their different
boiling points.
• As a liquid mixture is heated, the
substance with the lower boiling point will
vaporize first.
• Distillate: Condensed liquid substance

Mullis                    8
Kinetic Energy and Equilibrium
Vapor Pressure
In the beginning:
# particles condensing to liquid phase =
# particles evaporating to gas phase
• Increase temp            Increase kinetic energy
• Now, more molecules have enough energy to
leave the liquid.
• More vapor molecules = higher vapor pressure
• Equilibrium will soon be established, but at a
higher vapor pressure.
Mullis                  9
Phase Diagram
A phase diagram is a graph of pressure vs. temperature that
shows the conditions under which phases of matter exist.

Critical temp (Tc): Above this, the substance cannot exist in the liquid state.
Mullis                                    10
Four major "points" on a phase diagram

1. Triple point, TP - All three phases can exist in
equilibrium at this temperature and pressure.
(The solid-liquid line and the liquid-vapor line meet.)
2. Normal boiling point, Tb - The temperature at which
the vapor pressure of a liquid is equal to standard
atmospheric pressure.
(Standard atmospheric pressure line crosses the liquid-vapor
line.)
3. Normal melting point, Tm - The temperature at which
the vapor pressure of the solid and the vapor pressure
of the liquid are equal.
(Standard atmospheric pressure line crosses the solid-liquid
line.)
4. Critical temperature, Tc - The temperature above
which no amount of pressure will liquefy a vapor.
(The liquid-vapor line becomes vertical.)
Mullis                         11
Heating Curve at Constant
Pressure
Curve is flat during phase
changes.                                               Sample Heating Curve

Area A: Temperature
remains constant until                                                         Gas is
all the solid has become                    Exothermic                         warmed
B
liquid because melting

Temperature
Boiling
requires energy.
Once the energy is no                            A
longer required for                        Melting           Liquid is
phase change, kinetic                                        warmed
energy again increases.                     Solid is                          Endothermic
warmed