gases

• Kinetic-molecular theory


  Explains the behavior of solids, liquids, and gases in terms of particles in motion
• Kinetic-molecular theory


  • Gases consist of small particles separated by empty space
  • Gas particles are too far apart to experience significant attractive or repulsive forces
  • Gas particles are in constant random motion
  • Elastic collision is one in which no kinetic energy is lost
• Kinetic energy


  Energy due to motion
• Temperature


  Measure of the average kinetic energy of the particles in a sample of matter
• As temperature increases


  The rate of reaction increases
• Gases


  • Expand, diffuse, exert pressure, and can be compressed because they are in a low density state consisting of tiny, constantly-moving particles
• Diffusion


  Movement of one material through another
• Effusion


  Gas escaping through a tiny opening
• Graham's law of effusion


  1. Rate of effusion for a gas is inversely proportional to the square root of its molar mass

  2. Also applies to diffusion
• Pressure


  Force per unit area
• Gas pressure


  • Gas particles exert pressure when they collide with the walls of their container
  • There is less air pressure at high altitudes because there are fewer particles present, since the force of gravity is less
• Barometer


  Instrument used to measure atmospheric air pressure
• Pascal


  SI unit of force, equal to a force of one Newton per square meter
• Atmosphere


  Unit of pressure, equal to 760 mm Hg or 101.3 kilopascals
• Dalton's law of partial pressures


  The total pressure of a mixture of gases is equal to the sum of the pressures of all the gases of the mixture
• At a given temperature and pressure, the partial pressure of 1mol of any gas is the same
• Polar covalent bond


  A type of bond that forms when electrons are not shared equally
• Dispersion force


  Weak force that results from temporary shifts in density of electrons in electron clouds
• Dipole-dipole force


  Attraction between oppositely charged regions of polar molecules
• Hydrogen bond


  Special dipole-dipole attraction that occurs between molecules containing a hydrogen atom bonded to a small, highly electronegative atom with at least one lone pair of electrons
• Hydrogen bonds explain why water is a liquid at room temperature while compounds of comparable mass are gases
• Melting


  Occurs when heat flows into a solid object
• Melting point


  The temperature at which the forces holding the crystal lattice together are broken and it becomes a liquid
• Boiling point


  The temperature at which the vapor pressure of a liquid equals the atmospheric pressure