Chem Ch 11

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Chem Ch 11
2010-05-04 19:37:14
Chemistry Chang

Chang 11
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  1. Intermolecular forces
    • attractive forces between molecules
    • these forces come into play as the temp drops on a gas
    • the molecules slow until they do not have enough KE to overcome the attraction they have for each other
    • the gas will then condense
  2. Intermolecular forces vs. Intramolecular forces
    • Intermolecular forces are much weaker
    • Intramolecular forces hold atoms together in a molecule
  3. Intermolecular forces melt/boiling point trend
    the stronger the force, the higher the boiling point (and lower melting point)
  4. ion - dipole
    attract an ion and a polar molecule to each other
  5. dipole - dipole*
    • attractive forces between polar molecules
    • *van der Waals force
    • Dispersion will trump if it's a heavy molecule
  6. dipole - induced dipole*
    ion - induced dipole
    • the separation of pos and neg charges in the atom due to proximity
    • attractive forces a non polar molecule will have for a polar molecule due to proximity
    • *van der Waals force
  7. dispersion forces*
    • (Instantaneous dipole-induced dipole attraction)
    • an atom or non-polar molecule can, at an instance, be polar because of the movement of the electrons
    • *van der Waals force
    • increases with molar mass (more e-)
  8. Hydrogen bonding
    • dipole-dipole interation between the hydrogen atom in a molecule that is directly connected with a N, O or F and a N, O or F of another molecule
    • This results in a much higher b.p. and m.p. than expected
  9. phase
    a homogeneous part of the system in contact with other parts of the system, but separated from them by a well-defined boundary (ice cubes in water)
  10. polarizability
    • the ease with which the electron distribution in the atom can be distorted (induce a dipole)
    • the larger the # of e-'s the greater the polarizability
    • even molecules with dipoles can be polarized - causing them to be even more polar
  11. Ranking strength of intermolecular forces
    • Ionic compounds (not really inter, INTRA)
    • Hydrogen bonding
    • Larger mass
    • Same mass? Greater dipole moment (more polar molecule)
  12. surface tension
    • the amount of energy required to stretch or increase the surface of a liquid by a unit area
    • -strong intermolecular forces = high surface tension
    • water is stronger than most because of H bonding
  13. capillary action
    • tendency of a liquid to rise in narrow tubes or to be drawn into small openings
    • brought about by cohesion and adhesion
  14. adhesion
    an attraction between unlike molecules, ie. water and the sides of a glass tube
  15. cohesion
    the intermolecular attraction between like molecules, ie. water molecules want to cling to each other
  16. viscosity
    • a measure of a fluid's resistance to flow
    • strong intermolecular forces = high viscosity
    • weak " " = low viscosity
  17. special properties of water
    • can give off a lot of heat with only a slight decrease in temperature
    • solid form is less dense than liquid
    • each oxygen atom can form 2 hydrogen bonds
  18. crystalline solid
    possesses rigid and long-range order, atoms molecules or ions occupy specific positions
  19. amorphous solid
    • lack a well-defined arrangement and long range molecular order (no regular 3-D arrangement)
    • Example - plastics, glass
  20. unit cell
    basic repeating structural unit of a crystalline solid
  21. coordination number
    the number of atoms (or ions) surrounding an atom (or ion) in a crystal lattice
  22. Face-Centered cubic
    4atoms/unit cell
  23. Body-centered cubic
    2 atoms/unit cell
  24. Simple cubic
    1 atom/unit cell
  25. x-ray diffraction
    • the scattering of X-rays by the units of a crystalline solid
    • occurs because the wavelength of X-rays are around the same size as distance between lattice point of crystal
    • initially, the two beams are in phase
    • the upper wave is scattered by top layer
    • the bottom wave is scattered by the next layer
  26. Bragg equation
    • the distance a wave must travel to be in phase again
    • 2d sin @ = n h
    • h = wavelength, d = distance between planes, @ = theta, n = they will give, 1st order diffraction = 1
  27. Ionic Crystals
    • Contains ions
    • high melting points, brittle, poor conductor of heat and electricity
    • held together by electrostatic attration
    • lattice points are occupied by cations (small) and anions (big)
  28. Covalent Crystals
    • extensive 3-D network made entirely of covalent bonds
    • high melting points, poor conductor of heat and electricity
    • lattice points are occupied by atoms
    • examples: Diamond, graphite and quartz
  29. molecular crystals
    • Lattice points are occupied by molecules and are held together by van der Waals forces and/or H-bonding
    • melt at low temperatures (<100*C), soft, poor conductor or heat and electricity
    • Non-metals or metalloids
  30. Metallic Crystals
    • metals make up all the lattice points
    • usually dense, melt at a wide range of temps
    • good conductor of heat and electricity both in solid and liquid phase
  31. glass
    an optically transparent fusion product of inorganic materials that has cooled to a rigid state without crystallizing (like a really cool liquid)
  32. Evaporation or Vaporization
    • the process in which a liquid is transformed into a gas
    • this occurs when the molecules have enough energy to escape from the liquid surface
  33. vapor pressure
    the pressure of the evaporated gas molecules above a liquid
  34. condensation
    the change from the gas phase to the liquid phase
  35. equilibrium vapor pressure
    • the pressure obtained when the rate of evaporation equals the rate of condensation
    • increases with temperature
    • decreases as intermolecular forces increase
  36. dynamic equilibrium
    when the rate of a forward process is exactly balanced by the rate of the reverse process
  37. heat of vaporization
    • ^H vap - the energy required to vaporize one mole of a liquid
    • this is directly related to the strength of the intermolecular forces
    • the stronger the intermolecular forces, the highter the ^H vap
  38. Clausius-Clapeyron equation
    • shows the relationship between temperature and vapor pressure
    • In P = - ^H vap/RT + C
    • In (P1/P2) = (^H vap/R) (1/T2 - 1/T1)
    • R is 8.314 J/mol*K
  39. boiling point
    • the temperature at which the vapor pressure of a liquid is equal to the external pressure
    • vapor pressure and boiling point have inverse relationship (lower the pressure enough and water will boil at room temperature)
    • Normal boiling point is the vapor pressure at 1 atm
  40. freezing
    phase change from liquid to solid
  41. melting or fusion
    • phase change from solid to liquid
    • ^ H fus - molar heat of fusion - the energy required to melt one mole of a solid
  42. melting point and freezing point
    • it is the temperature at which the solid phase and liquid phase coexist in equilibrium
    • these are the same temperature for a substance
  43. critical temperature
    Tc - the temperature above which the gas cannot be made to liquelfy, no matter how great the applied pressure (highest temperature at whidch a substance can exist as a liquid)
  44. critical pressure
    Pc - the minimum pressure that must be applied to bring about liquifaction at the critical temperature
  45. heating curve
    • diagram showing phase changes from solid, to s&l equilibrium, liquid....
    • temp vs time
  46. equation for calculating heat change in terms of specific heat
    • q = m s ^t
    • t is in Celsius
  47. heat capactiy
    • C = ms
    • amount of heat required to raise the temperature of a given quantity of a substance by 1 degree Celsius
  48. sublimation
    • conversion of solid directly to vapor
    • ^H sub = ^H fus + ^H vap
  49. deposition
    conversion of vapor directly into solid phase
  50. phase diagram
    • summarizes the conditions at which a substance can exist as a solid, liquid or gas
    • plot of temperature and pressure
    • shows TRIPLE POINT - where all 3 phases can be in equilibrium with one another