1. Chapter 12
Intermolecular Forces:
Liquids, Solids, and Phase Changes

2. Intermolecular Forces: Liquids, Solids, and Phase Changes
12.1 An Overview of Physical States and Phase Changes
12.2 Quantitative Aspects of Phase Changes
12.3 Types of Intermolecular Forces
12.4 Properties of the Liquid State

3. ATTRACTIVE FORCES electrostatic in nature Intramolecular forces
bonding forces
These forces exist within each molecule.
They influence the chemical properties of the substance.
Intermolecular forces
nonbonding forces
These forces exist between molecules.
They influence the physical properties of the substance.

4. Phase Changes solid liquid gas exothermic sublimation vaporizing
melting
solid
liquid
gas
condensing
freezing
endothermic

5. A Macroscopic Comparison of Gases, Liquids, and Solids
Table 12.1
A Macroscopic Comparison of Gases, Liquids, and Solids
State
Shape and Volume
Compressibility
Ability to Flow
Gas
Conforms to shape and volume of container
high
Liquid
Conforms to shape of container; volume limited by surface
very low
moderate
Solid
Maintains its own shape and volume
almost none

6. Heats of vaporization and fusion for several common substances.
Figure 12.1
Heats of vaporization and fusion for several common substances.

7. Phase changes and their enthalpy changes.
Figure 12.2
Phase changes and their enthalpy changes.

8. A cooling curve for the conversion of gaseous water to ice.
Figure 12.3
A cooling curve for the conversion of gaseous water to ice.

9. Quantitative Aspects of Phase Changes
Within a phase, a change in heat is accompanied by a change in temperature which is associated with a change in average Ek as the most probable speed of the molecules changes.
q = (amount)(molar heat capacity)(T)
During a phase change, a change in heat occurs at a constant temperature, which is associated with a change in Ep, as the average distance between molecules changes.
q = (amount)(enthalpy of phase change)

10. Liquid-gas equilibrium.
Figure 12.4
Liquid-gas equilibrium.

11. A linear plot of vapor pressure- temperature relationship.
Figure 12.6
Figure 12.7
A linear plot of vapor pressure- temperature relationship.
Vapor pressure as a function of temperature and intermolecular forces.

12. The Clausius-Clapeyron Equation

13. SAMPLE PROBLEM 12.1
Using the Clausius-Clapeyron Equation
PROBLEM:
The vapor pressure of ethanol is 115 torr at 34.90C. If DHvap of ethanol is 40.5 kJ/mol, calculate the temperature (in 0C) when the vapor pressure is 760 torr.
PLAN:
We are given 4 of the 5 variables in the Clausius-Clapeyron equation. Substitute and solve for T2.
SOLUTION:
34.90C = 308.0K 1 T2
308K - ln
760 torr
115 torr
-40.5 x103 J/mol
8.314 J/mol*K =
T2 = 350K = 770C

14. Phase diagrams for CO2 and H2O.
Figure 12.8
CO2
H2O

15. Periodic trends in covalent and van der Waals radii (in pm).
Figure 12.10
Periodic trends in covalent and van der Waals radii (in pm).

18. Polar molecules and dipole-dipole forces.
Figure 12.11
Polar molecules and dipole-dipole forces.
solid
liquid

19. THE HYDROGEN BOND a dipole-dipole intermolecular force
A hydrogen bond may occur when an H atom in a molecule, bound to small highly electronegative atom with lone pairs of electrons, is attracted to the lone pairs in another molecule.
The elements which are so electronegative are N, O, and F.
hydrogen bond
donor
hydrogen bond
acceptor .. N H .. F O .. .. H O
hydrogen bond
acceptor
hydrogen bond
donor F H .. N ..
hydrogen bond
acceptor
hydrogen bond
donor

20. Dipole moment and boiling point.
Figure 12.12
Dipole moment and boiling point.

21. Hydrogen bonding and boiling point.
Figure 12.13
Hydrogen bonding and boiling point.

22. Polarizability and Charged-Induced Dipole Forces
distortion of an electron cloud
Polarizability increases down a group
size increases and the larger electron clouds are further
from the nucleus
Polarizability decreases left to right across a period
increasing Zeff shrinks atomic size and holds the electrons
more tightly
Cations are less polarizable than their parent atom because they are smaller.
Anions are more polarizable than their parent atom because they are larger.

23. Dispersion forces among nonpolar molecules.
Figure 12.14
Dispersion forces among nonpolar molecules.
separated Cl2 molecules
instantaneous dipoles

24. Molar mass and boiling point.
Figure 12.15
Molar mass and boiling point.

25. Molecular shape and boiling point.
Figure 12.16
Molecular shape and boiling point.
fewer points for dispersion forces to act
more points for dispersion forces to act

26. INTERACTING PARTICLES (atoms, molecules, ions)
Figure 12.17
Summary diagram for analyzing the intermolecular forces in a sample.
INTERACTING PARTICLES
(atoms, molecules, ions)
ions present
ions not present
ions only
IONIC BONDING
(Section 9.2)
nonpolar
molecules only
DISPERSION
FORCES only
polar molecules only
DIPOLE-DIPOLE
FORCES
H bonded to
N, O, or F
ion + polar molecule
ION-DIPOLE FORCES
polar + nonpolar
molecules
DIPOLE-
INDUCED DIPOLE
FORCES
HYDROGEN
BONDING
DISPERSION FORCES ALSO PRESENT

27. The H-bonding ability of the water molecule.
Figure 12.20
The H-bonding ability of the water molecule.
hydrogen bond donor
hydrogen bond acceptor

28. The Unique Nature of Water
great solvent properties due to polarity and
hydrogen bonding ability
exceptional high specific heat capacity
high surface tension and capillarity
density differences of liquid and solid states