Liquid-Vapor Equilibrium (Intermolecular Forces and Liquids and Solids) Green/Damji: 17.1 Chang: Chapter 11 Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Dec 17, 2015
Liquid-Vapor Equilibrium (Intermolecular Forces and Liquids and Solids)
Green/Damji: 17.1Chang: Chapter 11
Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display.
Eva
pora
tion
GreatestOrder
LeastOrder
11.8C
onde
nsat
ion
Focus on Evaporation and
Condensation
Write an equation for the equilibrium between liquid
water and its vapor:
Is evaporation an endothermic or exothermic
process?
The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation
H2O (l) H2O (g)
Rate ofcondensation
Rate ofevaporation=
Dynamic Equilibrium
11.8
Factors affecting the vapor pressure
• SURFACE AREA increasing surface area only means equilibrium is reached faster
• TEMPERATURE
Enthalpy of vaporization (DHvap) is the energy required to vaporize 1 mole of a liquid at its boiling point.
Enthalpy of vaporization : physical process (phase change) as
______________________: chemical reaction
11.8
The relationship between vapor pressure and temperature can be expressed mathematically – NOT req’d by IB
ln P = -DHvap
RT+ C
Clausius-Clapeyron Equation P = (equilibrium) vapor pressure
T = temperature (K)
R = gas constant (8.314 J/K•mol)
11.8
Vapor Pressure Versus Temperature
C = integration constant
The boiling point is the temperature at which the (equilibrium) vapor pressure of a liquid is equal to the external pressure.
The normal boiling point is the temperature at which a liquid boils when the external pressure is 1 atm.
11.8
The boiling point and enthalpy of vaporization are influenced by intermolecular forces…
Compound Enthalpy of vaporizationin kJ mol-1
Boiling Pointin K
Intermolecular Forces
methaneCH
4
9.0 109
methoxymethaneCH
3OCH
3
27.2 248
ethanolCH
3CH
2OH
38.6 352
State the relationship between intermolecular forces and enthalpy of vaporization.
State the relationship between intermolecular forces and boiling point.
A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas.
Phase Diagram of Water
11.9