Gas Laws
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  • 1. Gas Laws
  • 2. GAS LAWS They’ll save your life!
    • Boyle’s Law
    • Charles’s Law
    • Avogadro’s Law
      • Molar Volume
    • Combined Gas Law
    • Ideal Gas Law
  • 3. BOYLE’S LAW: Pressure & Volume
    • For a given mass of gas at constant temperature the volume (V) occupied by the gas is inversely proportional to the pressure (P) applied to the gas.
    • That means that Volume = 1/Pressure
    • A more useful expression also describes changes in volume and pressure, given by:
    • P i V i = P f V f
    • i = initial value of pressure or volume
    • f = final value of pressure or volume
  • 4. P i V i = P f V f High Pressure = Low Volume Low Pressure = High Volume Temperature does not change
  • 5. CHARLES’S LAW: Volume & Temperature
    • For a given mass of gas at constant pressure, the volume occupied by the gas is directly proportional to its absolute temperature .
    • That means that
    • Volume = Temperature x Some Constant
    • A more useful expression also describes changes in volume and temperature, given by:
    • V i /T i = V f /T f
    • i = initial value of pressure or volume
    • f = final value of pressure or volume
  • 6. V i /T i = V f /T f Pressure does not change As the temperature increases, the gas expands (volume  ). As Temperature decreases, the gas contracts (volume  ).
  • 7. AVOGADRO’S LAW: Equal Volumes
    • At the same temperature and pressure, equal volumes of gases contain equal numbers of molecules (or atoms for the Noble Gases).
    • That means that if temperature and pressure remain constant,
    • V i /n i = V f /n f
    • V = volume n = number of molecules
    • One of any gas contains 6.02x10 23 gas particles (Avogadro’s number)
  • 8. V i /n i = V f /n f Pressure and Temperature remain unchanged Increasing the number of moles of gas causes an increase in the volume needed to keep constant pressure and temperature.
  • 9. AVOGADRO’S LAW: Equal Volumes
    • Molar Volume – it follows from Avogadro’s law that the volume of a mole of any ideal gas at STP occupies the same volume as a mole of any other ideal gas at STP.
    • For ideal gases, this molar volume is 22.4 L @ STP (1 atm & 273K).
  • 10. 4 grams of He gas * 20 grams of Ne gas * 32 grams of O 2 gas * 46 grams of CO 2 gas * 1 mol of He gas * 1 mol of Ne gas * 1 mol of O 2 gas * 1mol of CO 2 gas *
  • 11. COMBINED GAS LAW
    • Boyle’s, Charles’s, & Avogadro’s Laws may be combined algebraically to yield the combined gas law:
    Temperature must be in Kelvin Pressure must be in atm, torr, Pa, or Kpa (but same for 1 & 2) Volume must be in mL, L, cm 3 , or dm 3 (but same for 1 & 2) n = the number of moles
  • 12. IDEAL GAS LAW
    • PV = nRT
    • Using the proportionalities in Boyle’s Charles’s, and Avogadro’s Laws:
    • V = constant x 1/Pressure (fixed mass & temperature)
    • V = constant x Temperature (fixed mass & pressure)
    • V = constant x moles (fixed pressure *temperature)
    • V = constant x 1/P x T x n
    • R is the ideal gas constant.
  • 13. IDEAL GAS CONSTANT
    • PV=nRT
    • P (atm,torr,Pa,Kpa) V (mL,L,cm3,dm3) = nRT (kelvin)
    • * Depending on the units you use, will choose an R to cancel the units*
    • R = 0.0821 L atm/K mol
    • R = 8.31 dm 3 kPa / K mol
    • R = 8.314 J/mol K
    • R = 62.36 L torr / mol K
  • 14.
    • Density = mass / volume
    • d = m/V
    • Substitute into ideal gas law:
    • PV=nRT
    • Molecular Weight = mass / moles
    • M = m/n
    • Substitute into ideal gas law:
    • PV=nRT
    IDEAL GAS LAW to solve for Gas Density & Molecular Weight
  • 15. GAS LAWS REVIEW
    • Boyle’s Law P i V i = P f V f
    • Charles’s Law V i /T i = V f /T f
    • Avogadro’s Law V i /n i = V f /n f
      • Molar Volume 22.4 L @ 1atm and 273 K
    • Combined Gas Law
    • Ideal Gas Law PV = nRT