The ideal Gas Equation

• Moles and gas volumes

  At the same temperature and pressure, equal volumes of different gases contain the same number of molecules. So when you measure a gas volume, you are indirectly counting the number of gas molecules (or the amount of gas in moles)
• Molar volume:

  The molar gas volume is the volume per mole of gas molecules at a stated temperature and pressure
• The volume of a gas depends on the pressure and temperature, but many experiments are carried out at room temperature and pressure (RTP)
• RTP is about 20 degrees Celsius and 101kPa (1 atm) pressure
• At RTP, 1 mole of gas molecules has a volume of approximately 24.0 dm3 = 24000 cm3
• Therefore at RTP the molar gas volume = 24.0 dm3 mol-1
• amount n (mol) = volume V / molar gas volume Vm
• Vm = 24.0 dm3 mol-1
• When V is in dm3: n = V (dm3) / 24.0
• When V is in cm3: n = V (cm3) / 24000
• The ideal gas equation: Room temperature and pressure will always be approximate, chosen to match typical conditions that experiments are carried out in
• There are the following assumptions for the molecules amking up an ideal gas:

  1. random motion
  2. elastic collisions
  3. negligible size
  4. no intermolecular forces
• What is the ideal gas equation?

  pV = nRT
• R = the ideal gas constant = 8.314 J mol-1 K-1
• Temperature is measured in K (Kelvin), which starts at absolute zero (-273 degrees C) Each 1K rise in temperature is the same as a I degrees C rise in temperature
• Volume in m3
• Pressure in Pa
• n = amount of gas molecules (mol)
• cm3 to m3?


  x 10-6
• dm3 to m3?


  X 10-3
• Degrees C to K?

  +273
• kPa to Pa?


  X 10^3