Transcript II.A. Phase Changes - Collier's Classroom

Liquids & Solids
Changes of State
Phase Changes
Phase Changes
 Evaporation
• molecules at the surface gain enough
energy to overcome IMF
 Volatility
• measure of evaporation rate
• depends on temp & IMF
Phase Changes
Boltzmann Distribution
temp
# of Particles
volatility
IMF
volatility
Kinetic Energy
Phase Changes
 Equilibrium
• trapped molecules reach a balance
between evaporation & condensation
Phase Changes
Pressure
• pressure of vapor above
a liquid at equilibrium
• depends on temp & IMF
• directly related to volatility
temp
v.p.
v.p.
 Vapor
IMF
temp
v.p.
Phase Changes
 Boiling
Point
• temp at which v.p. of liquid
equals external pressure
• depends on Patm & IMF
• Normal B.P. - b.p. at 1 atm
Patm
b.p.
IMF
b.p.
Phase Changes
 Melting
Point
• equal to freezing point
IMF
 Which
m.p.
has a higher m.p.?
polar
• polar or nonpolar?
• covalent or ionic?
ionic
Phase Changes
 Sublimation
• solid  gas
• v.p. of solid exceeds
external pressure at
or near room
temperature
 EX: dry ice, mothballs,
solid air fresheners