Part I: IMF and Properties of Liquids

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Part I IMF and Properties of Liquids

• CHM 102
• Monday, July 2nd

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IMFs continued H-bonding

• Hydrogen bonding can be thought of as a special
  case of dipole-dipole IMF.
• When a hydrogen is directly attached to an N, O,
  or F (Nof to remember it by), it renders the
  molecule to be capable of hydrogen bonding.
• The N-H, O-H, and F-H bonds are very polar, with
  a nearly naked positive charge on the hydrogen,
  and the partial negative charge on the N, O, or
  F.

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A view of H-bonding
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Find the H-Bonding Molecule(s)

• Of the following Choices, which can H-bond?
  H-Cl, CH4, NH3, CH3COOH, H-F, NO2, CH3CH2OH.

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IMF Continued Ion-Dipole

• The last IMF we havent spoken of is Ion-Dipole.
• This exists between an ion and the partial
  positive or negative side of a polar molecule.
• Note the trend here negative and opposite
  charges tend to form attractive IMFs.

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Tying it all Together

• What is the primary IMF for..
• CO2?
• H-F?
• CH3CH2CH3
• BF3
• Acetone (CH3COCH3) in water

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Properties of Liquids

• Many properties of substances are affected by
  IMF.
• Two such properties of liquids are viscosity and
  surface tension.
• Viscosity is the resistance of a liquid to flow.
  The greater the viscosity of a liquid, the harder
  it would be to pour. You might say a smoothie is
  more viscous than diet coke.

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Viscosity (contd)

• Viscosity can be though of as how easy it is for
  molecules of a substance to pass by one another.
  (Hence its related to IMF)
• If you look at the oils
• Hexane CH3CH2CH2CH2CH2CH3
• Heptane CH3CH2CH2CH2CH2CH2CH3
• Octane CH3CH2CH2CH2CH2CH2CH2CH3
• As the MW goes up, IMF (LDF only) goes up. As
  IMF goes up, the liquid resists pouring, and
  viscosity goes up.

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Surface Tension

• Have you ever seen a bug walk on water?
  Miraculous? No. Its surface tension.
• Water seems to behave almost like its got a
  pudding skin like effect at its surface.

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Rain-x and Surface Tension

• For those of you that have used Rain-x Have you
  noticed the water forms little spherical beads as
  it hustles off of the windshield?
• This is surface tension that causes this shape!
  Rain-x gives your windshield a smooth non-polar
  coating. So the water prefers to interact with
  itself (being polar) rather than the windshield
  (nonpolar).

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The Rain-xd Windshield
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Cohesive and Adhesive Forces

• Cohesive forces are forces that hold similar
  molecules together, like H-bonding holding water
  together, or dipole-dipole interactions holding
  together H-Cl(l).
• Adhesive forces tend to be between a substance
  and a surface.
• Lets compare the two forces.

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Cohesive vs. Adhesive
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Capillary Action
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Part II Phase Changes and Diagrams, Vapor
Pressure

• CHM 102
• Monday, July 2nd

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Phase Changes
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Melting (Fusion)

• If youre heating up a solid, as you add heat,
  the units that make up that solid vibrate in
  place until sufficient energy is added such that
  they can move freely with respect to one another.
• At this point fusion (or melting) has occured.
  The energy required to melt a substance is
  dependent upon its heat of fusion, or DHfus,
  typically given in kJ/mol.
• When ice cools water, it is the ice pulling the
  heat of fusion out of the water surrounding it
  that cools the drink.

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Vaporization (Boiling)

• As the temperature goes up for a liquid, the
  liquid molecules move more vigorously, and the
  vapor pressure (the pressure of the vapor phase
  of a liquid right at its surface) increases.
• When the vapor pressure equals the atmospheric
  pressure bearing down on the surface, the liquid
  begins to boil.
• To reach this point, a liquid must overcome the
  heat of vaporization, or DHvap.
• When you hop out of the ocean and your wet skin
  feels cool, youre really feeling the heat of
  vaporization being pulled from your skin to
  evaporate the water on your skin.

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DEMO TIME!
Whats going to happen to a soda can with 10 mL
of water in it when I heat it flaming hot with a
bunsen burner then quickly invert it in icy cold
water?
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Sublimation

• The heat of sublimation, or DHsub, is the energy
  required for a substance to sublime, or go from
  the solid directly to the gaseous state.
• The heat of sublimation is really just a sum of
  the heats of vaporization and fusion.
• When dry ice turns foggy (into gaseous CO2), it
  is subliming, and pulling the heat of sublimation
  from all around it, making it feel extremely cold.

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Heating Curves

• A heat curve shows the relationship between the
  heat added to a system and the temperature of the
  system.
• Below is a heating curve for water at a constant
  1 atm pressure.

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Practice Heating Curves

• If you heat 50 g of water from -20oC to 92oC, how
  much heat was added to the system? (DHfusion
  6.01 kJ/mol and DHvaporization 40.67 kJ/mol,
  specific heat of ice, liquid water, and steam
  are 2.09, 4.18, and 1.84 J/gK)

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Practice Heating Curves

• If you cool 1 mol of steam from 120oC to 42oC,
  what is the enthalpy change of the system?
  (DHfusion 6.01 kJ/mol and DHvaporization 40.67
  kJ/mol, specific heat of ice, liquid water, and
  steam are 2.09, 4.18, and 1.84 J/gK)

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Practice Heating Curves

• If you add 60.6 kJ of heat to 100 g of water at
  -30oC, what is the final temperature and state of
  the water? (DHfusion 6.01 kJ/mol and
  DHvaporization 40.67 kJ/mol, specific heat of
  ice, liquid water, and steam are 2.09, 4.18, and
  1.84 J/gK)

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Vapor Pressure

• Vapor pressure of a liquid is the pressure
  exerted by its vapor when the liquid and vapor
  states are in dynamic equilibrium.
• Dynamic equilibrium is when youve got two
  opposing processes occuring simultaneously.
• DEMO Foam ball demonstration.

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Vapor Pressure and Temperature

• As the temperature goes up, the vapor pressure of
  a liquid goes up.
• As T raises, the average kinetic energy of the
  liquid molecules raises, and the number of
  molecules with escape energy raises, so the
  vapor pressure raises.

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Vapor Pressure vs. Temperature for Water
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Vapor Pressure vs. TemperatureRelative
Volatility