Liquids and Solids
Changes of State
Objectives
1. Explain the relationship between equilibrium
and changes of state
2. Define Le Chatelier’s Principle.
3. Predict changes in equilibrium using Le
Chatelier’s Principle.
Dry Ice Balloon Explosion (Very Loud Bang) YouTube
Equilibrium
Equilibrium – a dynamic state in which two opposing
changes occur at equal rates in a closed system.
Changes of State
solid  liquid
melting
solid  gas
sublimation
liquid  solid
freezing
liquid  gas
vaporization
gas  liquid
condensation
gas  solid
deposition
An Equilibrium Equation
• Evaporation of a liquid
Liquid + energy  vapor
• Condensation of a liquid
Vapor  liquid + energy
• Liquid-vapor equilibrium
liquid + energy
vapor
Le Chatelier’s Principle
A system at equilibrium will shift to
offset a stress or change in conditions
imposed on the system.
Equilibrium and Temperature
liquid + energy
vapor
Change
Shift in Equilibrium
Increase in temperature
Decrease in temperature
Right
left
Equilibrium and Concentration
liquid + energy
Change
Addition of liquid
Removal of liquid
Addition of vapor
Removal of vapor
Decrease in container volume
Increase in container volume
vapor
Shift in Equilbrium
Right
Left
Left
Right
Left
right
Equilibrium Vapor Pressure
• Pressure exerted by a vapor in equilibrium
with its corresponding liquid at a given
temperature
-an increase in temperature causes an increase
in equilibrium vapor pressure; result of
increased K.E. of the liquid particles.
Volatile and Non-volatile liquids
• Volatile Liquid – a liquid
that readily evaporates at
room temp.; liquids with
low intermolecular forces.
Boiling
Boiling…
…occurs when the equilibrium vapor pressure of a
liquid equals the atmospheric pressure
…conversion of a liquid to a vapor within the liquid as
well as at the surface.
Normal Boiling Point: boiling point at standard
atmospheric pressure (100oC for water)
Boiling
Energy and Boiling
Molar Heat of Vaporization
• The amount of energy needed to vaporize
1 mole of a liquid at its boiling point
Freezing and Melting
Freezing:
Liquid  solid + heat energy
Melting:
Solid + heat energy  liquid
Normal freezing point: temperature at which a solid and
liquid are at equilbrium at standard pressure (0oC for
water
Molar Heat of Fusion – energy required to melt one mole
of a solid at its melting point.
Phase Diagram
Triple Point – temperature and pressure conditions
at which the solid, liquid, and gas phases of a
substance can coexist at equilibrium
Critical temperature - temperature above which a
substance cannot exist in the liquid phase.
Critical pressure – the lowest pressure at which a
substance can exist as a liquid at the critical
temperature.
Phase Diagram for CO2