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Gases pt.1
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  • 1. Pressure
    Pressure is force per unit area
    In the English system, pounds per square inch or psi
    Atmospheric pressure is about 14.7 psi
    Pressure = Force
    1 atm = 14.7 psi
    1 atm = 760 mmHg
    The mmHg is also called the Torr after Torricelli, inventor of the barometer
    SI unit of measurement, the pascal (Pa)
    1 Pa is the pressure exerted by a 0.1 mm high film of water on the surface beneath it
    The bar = 105 Pa
    1.013 bar = 1 atm = 760 mmHg = 14.7 psi = 100 kPa
  • 2. Gas Pressure Measurement
    The barometer measures pressure in terms of the height of a column on liquid mercury
    The atmosphere exerts a force on a pool of mercury, causing it to rise
    One standard atmosphere of pressure is a column of mercury 760 mm high
    Mercury is used to keep the column a manageable height
  • 3. Gas Pressure Measurement cont.
    The manometer measures gas pressure by differential
    The height of the column of liquid is proportional to the pressure
    Gas pressure can be more or less than atmospheric pressure
  • 4. Dalton’s Law of Partial Pressure
    Dalton’s law of partial pressures states that the sum of the partial pressures of gases sum to the total pressure of the gases when combined.
    Ptot = P1 + P2 + P3 + …
  • 5. Boyles’s Law
    The product of the pressure and volume for a trapped sample of gas = a constant (k)
    PV = k
    P1V1= P2V2 for analysis of a system before and after
  • 6. Sample Boyle’s Law problem
    A quantity of gas under a pressure of 106.6 kPa has a volume of 380 dm3. What is the volume of the gas at 103.3 kPa, if the temperature is held constant?
    P1 x V1 = P2 x V2
    (106.6 kPa) x (380 dm3) = (103.3 kPa) x (V2)
    V2 = 400 dm3
  • 7. Absolute Zero and the Kelvin Scale
    Absolute Zero is the temperature where all motion stops (-273C)
    For gases, the SI unit uses the Kelvin (K) scale.
    Kelvins = (273 + C)
  • 8. Charles’ Law
    The volume of each gas is directly proportional to temperature
    V = bT
    B = a constant
    V1/T1 = V2/T2
    Temperature is in Kelvins (273 + C)
  • 9. Charles’ Law Calculation
    At constant pressure, the volume of a gas is increased from 150 dm3 to 300 dm3 by heating it. If the original temperature of the gas was 20 oC, what will its final temperature be (oC)?
    T1 = 20 oC + 273 = 293 K
    T2 = X K
    V1 = 150 dm3
    V2 = 300 dm3
  • 10. Avogadro’s Law
    Volume is directly proportional to the number of moles of gas
    V = an
    V1/n1 = V2/n2
  • 11. The Combined Gas Law
  • 12. Sample Problem
    A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature(°C) of the gas at a volume of 90.0 mL and a pressure of 3.20 atm?