Kinetic Molecular Theory Do not take notes

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Kinetic Molecular Theory(Do not take notes)

• Composition structure of molecules affect the
  chemical physical properties of matter.
• Solids liquids have a lot of variation between
  both physical chemical properties.
• Gases, however, have very similar physical and
  chemical properties.

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Kinetic Molecular Theory

• Explains the behavior of gases in terms of
  particles in motion
• Assumptions
• Particles are very small with huge amounts of
  empty space between them (so no attractive or
  repulsive forces between them).
• Gas particles are in constant, random motion.
  Move in straight lines until they collide with
  each other or container walls. Collisions are
  elastic no energy is lost.
• Mass velocity affect the kinetic energy of
  individual gas particles (K.E. ½ mv2)

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Using KMT to explain gases

• Low density gases have extremely low densities
  because of the large spaces between gas molecules
• Compression expansion gases can be compressed
  if you decrease the space between gas molecules
  the random motion of gas particles will cause
  gases to expand to any space available
• Diffusion effusion both of these properties
  occur because of the constant random motion of
  gas particles and the lack of attractive or
  repulsive forces among gas particles.

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Gas Pressure

• Pressure is the force exerted compared to the
  area so lying down on ice spreads out your
  weight.
• Air pressure or atmospheric pressure is exerted
  in all directions since air is all around us
  moving randomly
• Measured with a barometer one ends a vacuum
  the other is open to the air
• Many units are used for pressure pascal, torr,
  psi and atmospheres are all common

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Intermolecular Forces of Attraction

• Occur between identical particles help explain
  how solids, liquids and gases exist at the same
  temperature
• Three main types dispersion, dipole-dipole and
  hydrogen bonds.
• All intermolecular forces are weaker than
  intramolecular forces (they have to be)

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Dispersion Forces

• The weakest intermolecular force
• Significant in nonpolar substances because no
  other intermolecular forces exist
• Explains why non-polar liquids are hard to pour
  and evaporate quickly (alcohols, gasoline, etc)

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Dipole-Dipole Forces

• Occur in polar molecules because permanent
  dipoles exist
• Molecules line up head to tail or positive region
  near a negative region
• Stronger than dispersion forces but weaker than
  hydrogen bonds

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Hydrogen bonds

• A special type of dipole-dipole bond
• Occur only between H and fluorine, oxygen or
  nitrogen
• Explains why water (18.00 g/mol) has such a huge
  surface tension and high boiling point while
  methane (16.05 g/mol) has very low surface
  tension and is a gas at room temperature

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Properties of liquids

• Liquid particles have random motion but greater
  attractive forces than gases, so liquids have a
  volume but no shape
• Density is also greater than gases while
  compression is much less since liquid particles
  are already close
• Liquids are less fluid than gases because they
  diffuse much slower due to the intermolecular
  forces interferring

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Properties of liquids

• Viscosity is the measure of the resistance of a
  liquid to flowing
• Viscosity is influenced by intermolecular forces,
  shape of the particle and temperature
• Year round oils actually change shape from
  spheres in cold weather to long strands when hot
  to increase viscosity

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Properties of liquids surface tension

• Particles at the surface have a greater downward
  pull than particles in the middle
• Greater intermolecular forces usually means
  greater surface tension
• Water forms a drop because of its high surface
  tension
• Surfactants are compounds that lower surface
  tension in a substance, like detergent in water

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Properties of liquids capillary action

• Occurs when water is placed in a container or
  substance that its highly attracted to
• If the attraction (adhesion) is greater than
  waters attraction to itself (cohesion),
  capillary action occurs.
• Like the downward curve you see when a liquid is
  in a glass
• When water is drawn up between the cellulose
  fibers of paper towels or the crystals in a diaper

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Properties of Solids

• According to KMT solids have as much kinetic
  energy at room temp as gases or liquids, but
  attractive forces are so great that particles in
  a solid move around a fixed point
• Most solids are more dense than liquids or gases
  (water is the exception)

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Phase Changes

• Most substances can exist in 1 of 3 states on
  Earth solid, liquid or gas depending on the
  pressure and temperature
• When energy is added or removed a substance may
  change from one phase to another
• KMT predicts this because as temperature
  increases, motion increases as forces of
  attraction can be overcome.

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Phase Changes that Require NRG

• Includes melting, vaporizing (boiling),
  evaporating and sublimation
• For melting, boiling and sublimation, the
  temperature plateaus where the phase change
  occurs because all incoming energy is being used
  to break bonds
• Stronger bond more energy higher boiling
  point or lower freezing point

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Evaporation

• When a liquid changes to a gas but only molecules
  at the surface escape to become vapor
• Occurs at a lower temperature than boiling point
  and is also a slower process than vaporization
• Explains why sweating cools us or other animals
  down

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Sublimation

• Process in which a solid goes directly to a gas
  without a liquid phase
• Iodine, dry ice, moth balls and air fresheners
  all tend to sublime
• Water (ice) will sublime if pressure is decreased
  like when ice cubes shrivel up in your freezer
• Freeze dried food is when food is frozen in a
  vacuum so the water sublimes. Makes food lighter
  and unable to grow bacteria.

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Phase Changes that release NRG

• Includes condensation, freezing, deposition
• Occurs when a vapor or liquid comes into contact
  with a cooler substance. The gas or liquid loses
  heat and if enough heat is lost, the forces of
  attraction become great enough to form a liquid
  or solid.
• This is why clouds form and why it warms up when
  it starts snowing
• Deposition is when a gas goes right to a solid
  like when it snows or frost forms

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Phase Diagrams

• Graphs pressure versus temperature
• Lines on diagram indicate where more than one
  phase exists
• Triple point is the temperature and pressure
  where all 3 states would exist or all 6 phase
  changes can occur
• Critical point pressure and temperature where
  water can not exist as a liquid regardless of an
  increase in temperature

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