1. Liquid-Vapor Equilibrium
(Intermolecular Forces and Liquids and Solids)
Copyright © The McGraw-Hill Companies, Inc.  Permission required for reproduction or display.

2. Evaporation and Condensation
Greatest
Order
Least
Focus on
Evaporation and Condensation
Write an equation for the equilibrium between liquid water and its vapor:
Is evaporation an endothermic or exothermic process?
Evaporation
Condensation
11.8

3. Before
Evaporation
At Equilibrium
11.8

4. The equilibrium vapor pressure is the vapor pressure measured when a dynamic equilibrium exists between condensation and evaporation
H2O (l) H2O (g)
Rate of
condensation
evaporation =
Dynamic Equilibrium
11.8

5. Factors affecting the vapor pressure
SURFACE AREA
increasing surface area only means equilibrium is reached faster
TEMPERATURE

6. What is the name of this diagram? Why is it important?
T2 > T1
What is the name of this diagram? Why is it important?
11.8

7. Vapor Pressure Versus Temperature
Patterns? Why?
11.8

8. 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

9. Vapor Pressure Versus Temperature
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)
C = integration constant
Vapor Pressure Versus Temperature
11.8

10. Why are there plateaus on this graph?
Heating Curve
Why are there plateaus on this graph?
11.8

11. 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

12. What are the three primary intermolecular forces?
List in order of increasing strength.

13. Enthalpy of vaporization Intermolecular Forces
The boiling point and enthalpy of vaporization are influenced by intermolecular forces…
Compound
Enthalpy of vaporization
in kJ mol-1
Boiling Point
in K
Intermolecular Forces
methane
CH4
9.0
109
methoxy
CH3OCH3
27.2
248
ethanol
CH3CH2OH
38.6
352

14. State the relationship between intermolecular forces and enthalpy of vaporization. State the relationship between intermolecular forces and boiling point.

16. A phase diagram summarizes the conditions at which a substance exists as a solid, liquid, or gas.
Phase Diagram of Water
11.9

17. Effect of Increase in Pressure on the Melting Point
of Ice and the Boiling Point of Water
11.9