Particle motion in gases

• • Particles in gas move randomly
  • Temperature related to average energy in kinetic energy store
  • Increasing temperature increases speed of particles
• • Collisions of gas particles on walls of sealed container cause exert force
  • Outward gas pressure in sealed container is total force exerted by all particles
  • Faster particles, more frequent collisions, increase in net force
  • So, increase in pressure (with constant volume)
• • Constant temperature whilst increasing volume can cause pressure to decrease
  • Particles more spread out and less frequent collisions
  • Pressure decreases
• • Pressure and volume are inverse proportional
  • Fixed mass and constant temperature:

  Pv = constant
• • Change in pressure causes change in volume
  • Force outside container due to pressure of gas around
  • Changes in size of container and changes in pressure can cause compression or expansion
  • Releasing a helium balloon causes it to rise
  • Atmospheric pressure decreases with height so pressure outside balloon decreases
  • Causes balloon to expand until pressure inside drops to same as atmospheric pressure
• • Doing work on a gas increases the internal energy of gas which increases temperature
  • Gas applies pressure to plunger of pump so exerts force
  • Work has to be done against force to push down plunge
  • This transfers energy to kinetic energy stores of gas particles, increasing temperature
  • If pump connected to tyre, increase in temperature