Particle model and pressure

• Describe the motion of molecules in gas

  They are in constant random motion
• What factor affects the average kinetic energy of gas molecules

  • the temperature of the substance
  • the higher the temperature the higher the average kinetic energy of the molecules
• What effect does increasing temperature have on the pressure of a gas when held at constant volume

  Pressure of the gas will increase as the temperature increases
• Why does pressure increase as temperature increases (at a constant volume)

  • Kinetic energy of molecules increases
  • collisions between molecules becomes more frequent
  • greater rate of change of momentum
  • greater force and therefore pressure
• If gas A is at a low pressure and gas B is at a high pressure what can be said about the rate of collisions in each gas

  • There are more collisions per second in gas B than gas A
  • the rate of collisions is higher in gas B
• Describe the force that the pressure of a gas exerts on the walls of its container

  • The net force acts at right angles to the containers surface
  • the force increases as pressure increases
• Explain how increasing the volume of a gas results in the decrease of pressure

  • Molecules become more spread out and so time between collisions increases
  • this reduces the rate of collisions
  • rate of change of momentum decreases, and so force exerted on container decreases , resulting in a lower pressure
• What can be said about the product of pressure and volume for a fixed mass of gas at a constant temperature 


  It’s constant

  p x v = constant
• What’s the units used for pressure

  Pascal (Pa)
• What increases when you do work on a gas

  • The internal energy of the gas
  • this can also lead to an increase of temperature
• Why does the temperature of air inside a bike pump increase when it’s pumped

  • Work is done on gas when it is compressed
  • doing work on a gas increases it’s internal energy, so also increases the average kinetic energy of the molecules
  • temperature increases with an increase of average kinetic energy