1. Phases of Matter
Particle Nature of Matter and Changes of State 4:19

2. Phases of Matter
MELTING POINT – solid and liquid phase can exist in equilibrium.
MELTING – At the melting point the particles once in a definite geometric pattern have
acquired rotational energy and are no longer part of a lattice structure.
Substance changes from the solid state to the liquid state.

3. change to a liquid at the standard pressure of 1 atmosphere.
Phases of Matter
Normal Melting Point - is the temperature at which a solid substance will
change to a liquid at the standard pressure of 1 atmosphere.
Normal Melting Point of H2O: 0oC or 273 K

4. Phases of Matter
FREEZING POINT – solid and liquid phase can exist in equilibrium.
FREEZING, SOLIDIFYING, CRYSTALIZING - changes from the liquid state to the solid state.

5. Phases of Matter
BOILING POINT - a liquid will boil at any temperature at which the vapor pressure equals
the atmospheric pressure on the liquid.
Normal Boiling Point is the temperature at which the vapor pressure of the liquid equals standard pressure (1 atm).
Normal Boiling Point of H2O: 100oC or 373 K

6. Phases of Matter CONDENSATION – change of phase from gas to liquid
- molecules of a gas can return to the
liquid phase merely by colliding with the
liquid surface, and becomes trapped by the
intermolecular attraction of the liquid.
Short animations on condensation

7. Phases of Matter VAPORIZATION - change of phase from liquid to gas
Liquid-Vapor Equilibrium =>
the rate of vaporization is equal to the rate of condensation.
These molecules exert a pressure called equilibrium vapor pressure.

8. VAPOR PRESSURE - increases as temperature of the liquid is increased (more molecules in vapor phase) and it is specific for each substance and temperature. (Table H)

9. EVAPORATION - process by which molecules of a liquid escape from the surface of the liquid and enter the vapor (gas) phase.
Substances that evaporate readily are considered to be volatile substances.

10. Remember temperature is proportional to
Evaporation occurs at a greater rate at higher temperatures because more molecules have enough energy to overcome the attractive forces between neighboring molecules and escape as vapor (gas).
Remember temperature is proportional to
average kinetic energy (avg.KE).

11. Solids that sublime at room temperature -
SUBLIMATION – change from the solid phase directly to the gaseous phase without passing through a liquid phase.
Solids which sublime have high vapor pressures and low intermolecular attractive forces.
Solids that sublime at room temperature -
carbon dioxide (dry ice), iodine crystals, and naphthalene (moth crystals)
CO2
JACS article on heat of sublimation

12. PHASE DIAGRAM

13. Phases of Matter, Bonding and Intermolecular Forces