Transcript II.A. Phase Changes

Ch. 12 - Liquids & Solids
III. Changes of State
(p. 372 - 382)
C. Johannesson
A. Phase Changes
C. Johannesson
A. Phase Changes
 Evaporation
• molecules at the surface gain enough
energy to overcome IMF
 Volatility
• measure of evaporation rate
• depends on temp & IMF
C. Johannesson
A. Phase Changes
Boltzmann Distribution
p. 477
temp
# of Particles
volatility
IMF
volatility
Kinetic Energy
C. Johannesson
A. Phase Changes
 Equilibrium
• trapped molecules reach a balance
between evaporation & condensation
C. Johannesson
A. Phase Changes
p.478
Pressure
• pressure of vapor above
a liquid at equilibrium
• depends on temp & IMF
• directly related to volatility
temp
v.p.
v.p.
 Vapor
IMF
C. Johannesson
temp
v.p.
A. 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
C. Johannesson
b.p.
A. Phase Changes
 Melting
Point
• equal to freezing point
IMF
m.p.
 Which
has a higher m.p.?
polar
• polar or nonpolar?
• covalent or ionic?
ionic
C. Johannesson
A. Phase Changes
 Sublimation
• solid  gas
• v.p. of solid equals
external pressure
 EX:
dry ice, mothballs,
solid air fresheners
C. Johannesson