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The Gas Laws

The Gas Laws. Pressure. Liquid pressure – exerted equally in all directions - swimmers feel an increase in pressure as they go deeper down into the ocean. Pressure. Atmospheric Pressure – (air pressure, barometric pressure)

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The Gas Laws

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  1. The Gas Laws

  2. Pressure Liquid pressure – exerted equally in all directions - swimmers feel an increase in pressure as they go deeper down into the ocean

  3. Pressure Atmospheric Pressure – (air pressure, barometric pressure) - at sea level, air pressure = weight of a kg mass on every square centimeter of surface exposed to it ** we are not conscious of air pressure because it is exerted in all directions

  4. Measuring Pressure Hg Barometer – measures AIR PRESSURE • Pressure varies with altitude • Decrease in air pressure as you increase altitude • Drop in air pressure before a storm • Normal Atmospheric Pressure - 760 mmHg or 1atm

  5. Measuring Pressure • 1 Atm = 760 mm Hg = 760 Torr= 101.3 kPa

  6. Measuring Pressure Manometer – measures pressure exerted by a gas in a closed container - 2 types – closed and open

  7. Measuring Pressure Closed Tube Manometer

  8. Gas Laws We will be studying the behavior of gases under varying conditions including: Pressure, Volume and Temperature Watch Safari Montage video - Common Properties of Gases http://econtent2.bucksiu.org/SAFARI/montage/play.php?frompage=play&keyindex=3139&location=local&chapterskeyindex=22429&sceneclipskeyindex=-1

  9. Kinetic Theory of Gases • Gas is made up of very small particles that are in constant random motion • Gas particles are free to spread far apart from each other • The higher the temperature – the faster the particles move

  10. Boyle’s Law •Safari Montage Video – Boyles Law http://econtent2.bucksiu.org/SAFARI/montage/playlistedit.php?playlisttype=MY&Action=MakeActive&playlistkeyindex=978&location=local • At constant temperature, the volume of a gas varies inversely with pressure P1V1 = P2V2

  11. Boyle’s Law •Safari Montage Video – Boyles Law http://econtent2.bucksiu.org/SAFARI/montage/playlistedit.php?playlisttype=MY&Action=MakeActive&playlistkeyindex=978&location=local • At constant temperature, the volume of a gas varies inversely with pressure P1V1 = P2V2

  12. Boyle’s Law Ex: What is the final pressure of 25.0 ml of a gas that was originally 38.3ml at a pressure of 765 mmHg?

  13. Charles’ Law • http://econtent2.bucksiu.org/SAFARI/montage/play.php?keyindex=3139&chapterskeyindex=22438&keyconceptskeyindex=74460&sceneclipskeyindex=-1&location=local At constant pressure, volume and temperature are directly related. V1 = V2or V1T2 = V2T1 T1 T2 *** Temp. MUST be in Kelvin

  14. Charles’ Law Ex: A balloon at 27.3 oC has a volume of 4.0 L. It is then heated to a temperature of 57.0 oC. What is the new volume of the balloon?

  15. Gay-Lussac’s Law • http://econtent2.bucksiu.org/SAFARI/montage/play.php?keyindex=3139&chapterskeyindex=22438&keyconceptskeyindex=74460&sceneclipskeyindex=-1&location=local • At constant volume, pressure and temperature are DIRECTLY related P1 = P2 or P1T2 = P2T1 T1 T2 *** Temp. MUST be in Kelvin

  16. Gay-Lussac’s Law Ex: A gas is left in a used aerosol can is at a pressure of 1.0 atm at 27.0 oC. If this can is thrown onto a fire, what is the internal pressure of the gas when it reaches 927 oC?

  17. Combined Gas Law The three laws we have learned can be combined into a single expression: P1V1 = P2V2 or P1V1T2 = P2V2T1 T1 T2 ** Where temperature MUST be in Kelvin

  18. Combined Gas Law Ex: A cylinder of compressed oxygen has a volume of 30.0L and 100.0 atm pressure at 27 oC. The cylinder is cooled until the pressure is 5.0 atm and the volume is 50 L. What is the new temperature of the gas?

  19. Ideal Gas Law http://econtent2.bucksiu.org/SAFARI/montage/play.php?keyindex=3139&chapterskeyindex=22438&keyconceptskeyindex=74448&sceneclipskeyindex=-1&location=local Ideal Gas – follows all the gas laws at ALL conditions of pressure and temperature. - Does not really exist. - Real gases usually start to liquefy at low temp. and high pressures. - We will use ideal gases for all problems in this class – therefore we will now learn the Ideal Gas Law

  20. Ideal Gas Law - Number of moles (n) is directly related to the volume of a gas PV = nRT Where: P = pressure V = volume n = number of moles R = ideal gas constant T = temperature (Kelvin)

  21. Ideal Gas Law R = ideal gas constant - number depends on the units of P,V and T 0.0821 L . Atm K . Mol 62.4 L. mmHg K. mol 8.31 L.kPa K.mol

  22. Ideal Gas Law Ex: A rigid hollow sphere of helium (680 L) is heated to 600K. The pressure increased to 18 atm. How many moles of helium does the sphere contain?

  23. Ideal Gas Law Ex: What is the pressure of 25.0 g of carbon dioxide that occupies a volume of 350 ml at 25 oC?

  24. Dalton’s Law of Partial Pressure Ex: What would be the pressure inside a cylinder if we combined these three gases?

  25. Dalton’s Law of Partial Pressure At constant volume and temperature, the pressure exerted by a mixture of gases is equal to the sum of the partial pressures. PT = P1 + P2 + P3 + …

  26. Dalton’s Law of Partial Pressure Ex: Air contains oxygen, nitrogen, carbon dioxide and trace amounts of other gases. What is the partial pressure of the oxygen gas given the following information? P of nitrogen = 593.4 mmHg P of carbon dioxide = 0.3 mmHg P of trace gases = 7.1 mmHg Total air pressure = 760 mmHg

  27. Graham’s Law of Diffusion Diffusion – movement of particles Which do you think would travel faster? A light gas (such as H) or a heavy gas (such as CO2)

  28. Graham’s Law of Diffusion Law says – rate of diffusion of a gas is inversely proportional to the square root of its formula mass. In other words: Lighter gas travel faster!!!!! Mathematically written: Rate A = √MB Rate B √MA

  29. Graham’s Law of Diffusion Ex: Which gas travels faster: CH4 or O2? Ex: How much faster does steam travel than carbon dioxide?

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