Gases

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Chapter 13
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Gases

• Kinetic-Molecular Theory of Gases

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• All particles are in constant motion.
• As temperature increases kinetic energy ?

increases
increases

• As gas particles move apart the volume ?

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Point Masses

• Gas particles are treated as a point with no
  volume and no mutual attraction
• -this is because theyre so small compared to
  the distances between them.

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Ideal Gases

• A theoretical gas with no volume and no
  attraction.
• A series of theories will be studied about ideal
  gases
• -standard pressure of 101.32 kPa
• -standard temperature of 0C or 273K
• -standard conditions are abbreviated

• STP

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Therefore

• Kinetic theory explains properties of gases based
  on a molecular view.
• The assumptions are
• The molecules are in continuous, random motion.
• A molecule has negligible volume.
• The forces between molecules are negligible.
• The average kinetic energy depends on the
  temperature.

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Four Gas Law Variables Are

• V volume
• P pressure
• T temperature
• n number of particles
• (Upper and Lower Case is important)

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Behavior of Gases

• Compression
• Expansion
• Diffusion movement of material from high to low
  concentration
• - lighter particles diffuse faster than heavier
  particles
• Effusion- gas escapes through a tiny opening

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Gas Pressure

• Pressure force/area
• Snowshoes in the snow force is spread out over
  a larger area
• Gas particles exert pressure as they collide with
  the walls of their container
• More particles in a given space, greater pressure
• Barometer is tool used to measure atmospheric
  pressure mercury rises or falls

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Units of pressure

• SI unit is Pascal (Pa)
• 1Pa 1 N/m2 derived from force
• 1atm 760mm Hg 760 torr 101.3 kPa 14.7 psi
• 1torr 1 mm Hg

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Daltons Law of Partial Pressure

• Total pressure of a mixture of gases is equal to
  the sum of all the pressures of the individual
  gases
• Pg. 392 practice problems

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Intermolecular Forces(between molecules)

• Dispersion Forces weak forces between temporary
  dipoles electron cloud is in constant motion
  (sometimes called London Forces).
• Dipole Dipole Forces forces between permanent
  dipoles (polar molecules).
• Hydrogen Bonds - a type of dipole-dipole
  attraction that occurs between molecules
  containing a hydrogen atom bonded to a small
  highly electronegative atom (oxygen, nitrogen, or
  fluorine)

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Liquids

• Denser than gases.
• Cant be easily compressed.
• Fluidity ability to flow (gases and liquids).
• Viscosity measure of the resistance to flow.
  Decreases with temperature.
• Surface Tension measure of the inward pull by
  particles in the interior (molecules at the
  surface have no attractions from above to balance
  the attractions from below).

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Liquids (continued)

• Capillary Action liquids in a narrow container
  form meniscus. This is caused by two forces
• Cohesion attraction between identical
  molecules.
• Adhesion attraction between different
  molecules.
• Example Adhesion between glass and water in a
  graduated cylinder is greater than cohesion
  between water molecules. Therefore water rises
  along the inner walls of the cylinder.

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Solids

• Density is greater than liquids
• Crystals orderly, geometric, 3-D structure.
• Atomic
• Molecular
• Covalent
• Ionic
• Metallic
• Amorphous not arranged in regular, repeating
  pattern

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Phase Changes

• That require energy
• Melting
• Vaporization (Evaporation)
• Sublimation
• That release energy
• Freezing
• Condensation
• Deposition