CHAPTER 11: Intermolecular Forces, Liquids, and Solids Are there any IDEAL GASES? The van der Waals equation corrects for deviations from ideality Does the KMT break down? Kinetic Molecular Theory 1. Gas molecules are greatly separated. (Volume
of particles is negligible) 2. Gas molecules are in constant random motion. 3. The average kinetic energy is determined by temperature. 4. Collisions between the gas molecules with one another or with the walls of the container are perfectly elastic. 5. Attractive and repulsive
forces between gas molecules are negligible. non-elastic collisions are caused by intermolecular forces and lead to the liquid (and solid) states At low temp. and high pres. all gases condense!!!!
Intermolecular Forcesforces that operate between molecules and/or ions and that are responsible for the existence of liquid and solid phases. FIGURE 11.12 They Include:
-Ion-Ion -Ion-Dipole -Dipole-Dipole
-Hydrogen Bonding (special type of dipoledipole) - London Dispersion Forces (Induced Dipole- Induced Dipole)
Phase Diagram- a plot of Pressure vs Temperature in which the solid, liquid, and gas regions and the equilibria between these regions are shown.
(Dynamic)Equilibrium - a condition that exists when two opposing processes (either physical or chemical ) occur at the same rate. An equilibrium is indicated by the following symbol, Triple Point - the pressure and temperature point at
which solid, liquid, and gas phases are all present and in equilibrium. Critical Point- temperature and pressure point which is the highest temperature at which the liquid phase can exist. There is no liquid phase above the critical temperature or below the triple point. From phase diagram
-does CO 2 boil at 1 ATM -does liquid exist below 5.11ATM How do the melting points of CO 2 and water differ as a function of pressure? P/ T > 0, normal behavior, solid phase is
more dense than liquid P/ T < 0, very rare, solid phase is less dense than liquid (WATER!!!!!!!!!!!!!) What are implications of this fact for water? An increase in pressure (at constant temperature) along the SOLID-LIQUID equilibrium line causes a shift to the more dense phase (normally the solid).
Energetics of Phase Transformations Heat of Fusion, H fus, - amount of heat necessary to convert a given quantity of solid to liquid. (for ice, 333J/g) Heat of Vaporization, H vap - amount of heat needed to convert a given quantity of liquid to gas. (for water, 2260J/g) H sub = H fus + H vap
Boiling Point- temperature at which the vapor pressure is equal to the applied pressure. Normal Boiling Point refers to one ATM. Vapor Pressure - the
pressure of a gas in contact with its liquid or solid phases in a sealed container.
Along L/G, (vapor pressure curve) rate of evap. = rate of cond.
Rate of Evaporation depends on: -surface area -Temperature -nature of cpd. (volatile or non-volatile)
Normally bp increase as MW increases for related sets of compounds unless Hydrogen Bonding is present.
Hydrogen Bonding- an unusually strong dipoledipole force which occurs when hydrogen is bound to a small electronegative
atom (N, O, or F). Accounts for the unusually high boiling points of NH 3,H 2 O, and HF.
Other Properties of Liquids -Viscosity (Gases too) -Surface Tension -Capillary Action adhesive vs cohesive forces SOLIDS -crystalline have long
range order (salt, sugar, diamond) -amorphous lack long range order (glass, rubber) unit cell-the smallest repeating unit of a crystalline solid consider primitive, body centered, and face centered cubic
TABLE 11.7 Summarizes all information on different types of Solids: -Ionic (ionic cpds) -Metallic (metals) -Molecular (covalent) -Network (diamond, graphite, and quartz).
Be able to predict properties of a solid based
on its classification. (Table 11.7) -melting point -electrical cond. -malleable -hardness
Circle the member of the following which has... hydrogen bonding a) H 2 or HF b) NH 3 or PH 3 higher boiling point c) HCl or HBr d) H 2 O or H 2 S higher velocity e) N 2 (300K) or N 2 (400K) f) N 2 or O 2 (both at 300K) greater malleability g) Au or AuCl
higher melting point h) KCl or Cl 2 higher electrical conductivity i) CaCl 2 (s) or Ca(s) greater hardness j) SiO 2 CO 2 or