Hydrogen Bonding

1
Hydrogen Bonding

• Interaction btwn e--rich atom connected to H
  entity another H attached to erich atom
• e--rich atom O, F, N
• Gives water gt density than ice
• Ice floats
• Higher heat capacity

2
Hydrogen Bonding

• Unique properties
• B.p. of H2O, HF, and NH3 much higher

3
Boiling Point

• Bp ? temp. at which vapor pressure external
  (atmospheric pressure)
• At higher elevations atmospheric pressure is
  lower ? water boils less than 100 C

4
Surface Tension

• Outer molecules interact with surface, while
  inner interact with other molecules
• It has a skin
• Skin toughness surface tension
• E required to break through surface
• Smaller surface area reason that water drops
  spherical
• http//www.ilpi.com/genchem/demo/tension/demo

5
Capillary Action

• When water goes up a small glass tube
• Due to polarity of Si-O bonding with water
• Adhesive forces gt cohesive forces of water
• Creates a chain or bridge
• Pulls water up tube
• Limited by balancing gravity with
  adhesive/cohesive forces
• Thus, water has a concave meniscus

6
Mercury

• Forms a convex meniscus
• Doesnt climb a glass tube
• Due to cohesive forces gt adhesive forces

7
Viscosity

• Hydrogen-bonding increases viscosity
• But large non-polar liquids like oil have
• 1) large unwieldy molecules w/greater
  intermolecular forces
• 2) greater ability to be entangled w/one another

8
Sublimation

• Going from solid to gas without going through the
  liquid state
• Enthalpy of sublimation ?H?sublimation
• Iodine, dry ice (solid CO2) ice sublimate
• Frost on grass on a cold morning sublimates

9
Polymers

• Huge molecules with repeating monomers (subunits)
• Thermoplastics (polyethylene) respond to heating
• Soften and flow when heated, harden when cooled
• Thermosetting plastics (Formica) initially soft,
  but solid when heated irreversible

10
Disturbing chemical equilibria

• Le Chateliers Principle
• Change one component of the rxn,
• The rxn will attempt to rectify it
• (rectify is not a bad word)
• Think of it this way
• If something is changed, how can it be undone or
  controlled?

11
Temperature variation on equilibrium

• 2NO2(g) ? N2O4(g) heat
• Exothermic ? heat out
• Raise the temp to 298 K ? will want to get rid of
  excess heat ? will swing to left ? producing more
  NO2 (endothermic)
• Sooner or later, equilibrium re-established

12
Pressure volume change on equilibrium

• If volume decreased (pressure increased) ? favors
  smaller of molecules
• If volume increased (pressure decreased) ? favors
  larger of molecules
• If reversible rxn has of molecules on each
  side, a volume/pressure change will do nothing