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

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

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.

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

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

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

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

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.

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)

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

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.

The Clausius-Clapeyron Equation

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

Phase diagrams for CO2 and H2O. Figure 12.8 CO2 H2O

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).

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

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

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

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

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.

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

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

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

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

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

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