Kinetic theory

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  • 1. Gases Part 1: Kinetic Molecular Theory
  • 2. Kinetic Molecular Theory
    • describes the behavior of gases in terms of particles in motion.
    • makes several assumptions about the
      • size
      • motion, and
      • energy of gas particles.
  • 3. Assumptions
    • Particle size
    • Particle motion
    • Particle energy
  • 4. Particle Size
    • Gases consist of small particles that are separated from one another by empty space.
    • The volume of the particles is small compared with the volume of the empty space.
  • 5. Gas has Mass
  • 6. Particle motion
    • Gas particles are in constant, random motion.
    • Particles move in a straight line until they collide with other particles or with the walls of their container.
  • 7. Elastic Collisions
    • Collisions between gas particles are elastic.
    • An elastic collision is one in which no kinetic energy is lost.
  • 8. Particles move very fast
  • 9. Particle energy
    • Kinetic energy is a function of the mass and speed of a particle.
    • In a sample of a single gas, all particles have the same mass but all particles do not have the same velocity.
    • Therefore, all particles do not have the same kinetic energy.
  • 10. Kinetic Energy and Momentum
  • 11. Properties of Gases
    • Low density
    • Compressible
    • Diffuses
  • 12. Low density
    • Density – mass per unit of volume (g/cm 3 )
    • Density of gasses is much lower than the density of solids or liquids.
  • 13. Compressible
    • Gasses can be compressed
    • Compression – can be pushed into a smaller volume
    • Expansion – can be pulled into a greater volume
  • 14. Diffusion
    • the movement of one material through another.
    • particles diffuse from an area of high concentration to one of low concentration
  • 15. Temperature and Pressure
    • Kinetic theory explains the temperature and pressure of gasses
      • How fast the molecules of a gas are going
      • How heavy the molecules are
  • 16. Temperature
    • Temperature is a measure of the average kinetic energy of the particles in a sample of matter.
  • 17. In other words…
    • Temperature is related to
      • How fast the molecules of a gas are moving
      • How often the molecules hit the walls of the container
  • 18. Gas has temperature
  • 19. Pressure
    • defined as force per unit area.
    • Gas particles exert pressure when they collide with the walls of their container.
  • 20. In other words…
    • Pressure is related to
      • How fast the molecules of a gas are moving
      • How much the particles weigh
      • How hard the molecules hit the walls of the container
  • 21. Gas has pressure
  • 22. Measuring Pressure
    • A barometer is an instrument used to measure atmospheric pressure.
    • A manometer is an instrument used to measure gas pressure in a closed container.
  • 23. Pressure Units
    • SI unit of pressure is the pascal (Pa). It is named for Blaise Pascal.
    • One pascal is equal to a force of one newton per square meter: 1 Pa= 1 N/m 2 .
  • 24. Other Pressure Units
    • engineers often report pressure as pounds per square inch (psi).
    • pressures measured by barometers and manometers can be reported in millimeters of mercury (mm Hg).
  • 25. Air pressure
    • At sea level, the average air pressure is 760 mm Hg when the temperature is 0°C.
    • Air pressure often is reported in a unit called an atmosphere (atm). One atmosphere is equal to 760 mm Hg or 760 torr or 101.3 kilopascals (kPa).
  • 26. Temperature and Pressure
    • Temperature and pressure are directly proportional
    • As one goes up, the other goes up
    • As one goes down, the other goes down
  • 27. Temperature and Pressure
  • 28. Temperature and volume
  • 29. Volume and Pressure