PHASE CHANGES

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

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

Condense Freeze Melt Evaporate Solid Liquid Gas

Deposition Sublimation Solid Liquid Gas

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

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 http://youtu.be/wV7g8L633Sg The maze - http://www.dailymail.co.uk/sciencetech/article-2442638/Leidenfrost-Effect-makes-high-temperature-water-travel-uphill.html

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.

Phase Changes of Water

Another Phase Diagram Cyclohexane near triple point

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)

SIMULATION http://phet.colorado.edu/en/simulation/states-of-matter