Temperature & pressure

• Molecules in a Gas

  Motion of Particles in a Gas

  • Molecules in a gas are in constant random motion at high speeds
  • Random motion means that the molecules are travelling in no specific path and undergo sudden changes in their motion if they collide:
  • With the walls of its container
  • With other molecules
  • The random motion of tiny particles in a fluid is known as Brownian motion
• Pressure

  • Molecules of gas in a container will collide with the container walls
  • Pressure is defined as the force exerted per unit area 
  • P=f/a
  • Pressure = force / area
• • Pressure is measured in the units Pascals (Pa)
  • The area should always be the cross-sectional area of the object
  • This means the area where the force is at right angles to it
• 
  

  • The molecules in the gas move around randomly at high speeds, colliding with surfaces and exerting pressure upon them
  • The temperature of a gas is related to the average speed of the molecules:
  • The hotter the gas, the faster the molecules move and vice versa
  • Hence, the molecules collide with the surface of the walls more frequently and with more force
  • This increases the pressure
• Temperature & Pressure

  • The motion of molecules in a gas changes according to the temperature
  • As the temperature of a gas increases, the average speed of the molecules also increases
  • The hotter the gas, the higher the average kinetic energy
  • The cooler the gas, the lower the average kinetic energy
  • If the gas is heated up, the molecules will travel at a higher speed
  • This means they will collide with the walls more often
  • This creates an increase in pressure