Changes of State Phase Changes Phase Changes u

Changes of State

Phase Changes

Phase Changes u Evaporation • molecules at the surface gain enough energy to overcome IMF u Volatility • measure of evaporation rate • depends on temp & IMF

Phase Changes u Equilibrium • trapped molecules reach a balance between evaporation & condensation

Phase Changes p. 478 u Vapor Pressure v. p. • pressure of vapor above a liquid at equilibrium • depends on temp & IMF • directly related to volatility temp v. p. IMF temp v. p.

Phase Changes u 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 u Melting Point • equal to freezing point IMF u Which m. p. has a higher m. p. ? polar • polar or nonpolar? • covalent or ionic? ionic

Phase Changes u Sublimation • solid gas • v. p. of solid equals external pressure u EX: dry ice, mothballs, solid air fresheners

Heating Curves Gas - KE Boiling - PE Liquid - KE Melting - PE Solid - KE

Heating Curves u Temperature Change • change in KE (molecular motion) • depends on heat capacity u Heat Capacity • energy required to raise the temp of 1 gram of a substance by 1°C • “Volcano” clip - water has a very high heat capacity

Heating Curves u Heat of Vaporization ( Hvap) • energy required to boil 1 gram of a substance at its b. p. • usually larger than Hfus…why? u EX: sweating, steam burns, the drinking bird

Heating Curves u Phase Change • change in PE (molecular arrangement) • temp remains constant u Heat of Fusion ( Hfus) • energy required to melt 1 gram of a substance at its m. p.

Phase Diagrams u Show the phases of a substance at different temps and pressures.