DO YOU REMEMBER: Vaporization? Evaporation? Condensation? Sublimation? Deposition? Potential Energy changes? Kinetic Energy changes? Triple Point?

Equilibrium: A dynamic condition where two opposite changes occur at equal rates Evaporation Equilibrium

Vapor Pressure pressure exerted by a vapor over its liquid. Liquids in which IMFs are strong have lower vapor pressures. Vapor pressure increases significantly with temperature.

ΔH vap : Molar Heat of Vaporization Amount of heat needed to vaporize one mole of a given liquid q p = n·ΔH vap

If ΔH vap of oxygen is 3.41 kJ/mol, how much energy is needed to vaporize 4 moles of oxygen? Problem: kJ

If ΔH vap of water is 40.7 kJ/mol, how much energy is needed to vaporize 50g water? H 2 O (l)  H 2 O (g) Problem: 113 kJ

John A. Schreifels Chemistry 211 Chapter 11-7 There is a relationship between vapor pressure and temperature: The Clausius – Clapeyron equation can be used for any two pairs of points. P vap = vapor pressure ΔH vap = enthalpy of vaporization R = J/K·mol T = temperature (in Kelvin) Clausius – Clapeyron Equation

Problem: The vapor pressure of water at 25°C is 23.8 torr, and the heat of vaporization of water at 25°C is 43.9 kJ/mol. Calculate the vapor pressure of water at 65°C. ln (23.8 torr) = [ J/mol ] [ 1 – 1 ] (P vap,T2 ) [ J/K·mol][338 K 298 ] P vap,T2 = 194 torr

Molar Heat (enthalpy) of Fusion: ΔH fus Amount of heat needed to melt one mole of a solid q p = n·ΔH fus

Problem Which would you predict should be larger for a given substance:  H vap or  H fus ?

Vapor Pressure solids also have vapor pressure

supercooled can stay liquid below melting point because doesn’t achieve level of organization needed to make solid superheated when heated to quickly, liquid can be raised above boiling point causes “bumping”