Work on a gas

• 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
• • If a gas is allowed to expand, the gas will do work instead
  • This causes the gas to lose energy, which results in a decrease in temperature
• Increasing Temperature

  • An example of doing work on an enclosed gas that leads to an increase in its temperature is a bicycle pump
  • If a thumb is placed on the end of a bicycle pump and it is quickly compressed several times, it will be able to feel the pump getting very warm
  • This is because work is done on the gas, causing its temperature to rise
• Decreasing Temperature

  • When pressurised carbon dioxide is released from a high-pressure cylinder, the gas does work, which means it loses energy
  • This can cause the carbon dioxide to freeze, forming dry ice

  The sudden expansion of carbon dioxide from a cylinder can rapidly cool it, forming dry ice (solid CO2)