Week 1 - Behavior of Gases

• In Kinetic Molecular Theory, particles in an ideal gas:

  • have no volume
  • have elastic collisions
  • are in constant, random, straight-line motion
  • don't attract or repel each other
  • have an average KE related to Kelvin temperature
• Characteristics of Gases

  1. Gases expand to fill any container with random motion and no attraction
  2. Gases are fluids like liquids, no attraction
  3. Gases have very low densities, no volume = lots of empty spaces
• Characteristics of Gases

  4. Gases can be compressed

  5. Gases undergo diffusion and effusion in random motion

  
• Always use absolute temperature (Kelvin) when working with gases.
• Pressure = force/area
• Pressure

  • Barometer measures atmospheric pressure e.g. mercury barometer

  
• Pressure

  • manometer measures contained gas pressure e.g. u-tube manometer

  
• Standard Temperature and Pressure (STP)

  • 0 degree celsius or 273 K
  • 1 atm or 101.325 kPa
• The relationship between the volume of a gas and its pressure was analyzed by Robert Boyle in 1662. He found that the volume of the gas decreases as the pressure exerted on it increases.
• In Boyle's Law, the pressure and volume of a gas are inversely related, at constant mass and temperature.
• In 1787, Jacques Charles studied the relationship between the volume and temperature of a gas using a balloon. He concluded that the volume of a gas is directly proportional to its temperature.
• In Charles' Law, the volume and absolute temperature (K) of a gas are directly related at constant mass and pressure.
• Gay Lussac's Law

  • The person who is credited with the determination of the temperature-pressure relationship in gases at constant volume is Joseph Louis Gay-Lussac.
  • He deducted that the pressure of a gas is directly proportional to its temperature.
• Combined Gas Law

  • combines the 3 gas laws: Boyle's, Charles' and Gay-Lussac's Law
  • states that the ratio of the product of pressure and volume and the absolute temperature of a gas is equal to constant.
• When Avogadro's Law is added to the combined gas law, the Ideal Gas Law results.
• Unlike the named gas laws, the Combined Gas Law doesn't have an official discoverer. It is simply a combination of the other gas laws that works when everything except temperature, pressure, and volume are held constant.