1. PHASE CHANGES

2. Phases of Matter Solid – strong IMF, definite shape & volume
Liquid – medium IMF, varied shape, definite volume
Gas – weak IMF, varied shape & volume
Plasma – electrons dissociated from nucleus (Northern Lights, space)
Example

4. Phases of Matter Depends on…
IMF – Hydrogen bonds, Dipole, London dispersion (van der Waals)
Temperature – average kinetic energy
Changing phases requires energy to be released or absorbed
Pressure – molecular collisions

5. Condense
Freeze
Melt
Evaporate
Solid
Liquid
Gas

6. Deposition
Sublimation
Solid
Liquid
Gas

7. Phase Changes Variations among substances
Boiling occurs when vapor pressure (pressure to become vapor) = atmospheric pressure
Change in atmospheric pressure changes boiling & freezing points
Volatile liquids have a high VP and weak IMF resulting in low boiling points

9. Leidenfrost Effect
Liquid in contact with something hotter than liquid’s boiling point will produce an insulating vapor layer that keeps the liquid from boiling rapidly
The maze -

10. WATER
Often easiest to look at since all three phases can occur at atmospheric pressure
Hydrogen bonding results in key features of water
Cohesion, adhesion, high heat capacity, solvent, etc.

11. Phase Changes of Water

12. Another Phase Diagram
Cyclohexane near triple point

13. Supercritical Fluids - VIDEO
No longer a difference in density so can’t tell the difference between the phases
Liquid density drops b/c thermal expansion (V&T)
Gas density increases b/c increased pressure (V&P)

14. SIMULATION