3.3.1 Particle Motion in Gases

• The molecules of a gas are in what?

  Constant random motion.
• The temperature of a gas is related to what?

  The average kinetic energy of the molecules.
• Changing the temperature of a gas, held at a constant volume, changes what?

  The pressure it exerts.
• Why do both pressure and temperature increase when a gas is held at a constant volume?

  • Kinetic energy of molecules increases
  • Collisions between molecules become more frequent
  • Greater rate of change of momentum
  • Greater force and therefore pressure
• If gas A is at a low pressure, and has 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 in gas A and therefore 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 container’s surface.
  • The force increases as pressure increases.
• Explain how increasing the volume of a gas results in a 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 forces exerted on container decreases, resulting in a lower pressure
• What is the formula for pressure?

  Pressure = force / area.
• What factors can increase the pressure of a gas?

  Faster moving particles and more collisions with the walls of the container.
• How do temperature and concentration affect a flexible container?

  Some containers, such as balloons, are flexible. An increase in force on the walls of the container would just cause the container to expand. Therefore, changing temperature or concentration will change the volume of the container, rather than the pressure of the gases inside.