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BEHAVIOR OF GASES

BEHAVIOR OF GASES. Gases have mass Gases have volume (take up space) Gases exert pressure Gases fill their containers

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BEHAVIOR OF GASES

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  1. BEHAVIOR OF GASES Gases have mass Gases have volume (take up space) Gases exert pressure Gases fill their containers Gases are mostly empty space (the molecules in a gas are separate, very small, and very far apart) Gases doing all of these things!

  2. Kinetic Theory of GasesThe basic assumptions of the kinetic molecular theory are: Gases are mostly empty space The molecules in a gas are separate, very small and very far apart

  3. Kinetic Theory of GasesThe basic assumptions of kinetic molecular theory are: Gas molecules are in constant, chaotic motion Collisions between gas molecules are elastic (there is no energy gain or loss during a collision)

  4. Kinetic Theory of GasesThe basic assumptions of the kinetic molecular theory are: The average kinetic energy of gas molecules is directly proportional to the absolute temperature Gas pressure is caused by collisions of molecules with the walls of the container

  5. Measurements of Gases To describe a gas, its volume, amount, temperature, and pressure are measured. Volume: measured in L, mL (1 mL = 1 cm3) Amount: measured in moles (mol) or grams (g) Temperature: always measured in KELVIN (K) K = ºC + 273 Pressure: measured in mm Hg, torr, atm, etc. P = F / A (force per unit area)

  6. Moderate Force (about 100 lbs) Small Area(0.0625 in2) P = F /A Enormous Pressure (1600 psi)

  7. Bed of Nails Moderate Force Small Pressure P = F / A Large Surface Area(lots of nails)

  8. Units of Pressure Units of Pressure: 1 atm = 1 atmosphere 1 atm = 760 mm Hg 1 atm = 760 torr 1 atm = 1.013 x 105 Pa 1 atm = 101.3 kPa 1 atm = 1.013 bar 1 atm = 14.7 p.s.i. (pounds per square inch)

  9. Boyle’s Law For a given number of molecules of gas at a constant temperature, the volume of the gas varies inversely with the pressure. As P, V (or vice versa) INVERSE RELATIONSHIP (when T and amount of gas (n) are constant) V  1/P P1V1 = P2V2

  10. Example: A sample of gas occupies 12 L under a pressure of 1.2 atm. What would its volume be if the pressure were increased to 3.6 atm? (assume temp is constant) P1V1 = P2V2 (1.2 atm)(12 L) = (3.6 atm)V2 V2 = 4.0 L

  11. Charles’ Law Jacques Charles (1746-1828) The volume of a given number of molecules is directly proportional to the Kelvin temperature. As T, V  (or vice versa) DIRECT RELATIONSHIP (when P and amount (n) are constant) V  T

  12. Example: A sample of nitrogen gas occupies 117 mL at 100.°C. At what temperature would it occupy 234 mL if the pressure does not change? (express answer in K and °C) V1 / T1= V2 / T2 (117 mL) / (373 K) = (234 mL) / T2 T2 = 746 K T2 = 473 ºC

  13. Law of Gay-Lussac As the temperature of an enclosed gas increases, the pressure increases, if the volume is constant As T, P, (or vice versa) DIRECT RELATIONSHIP V  T

  14. The gas used in and aerosol can is at a pressure of 103 kPa at 25 C. If the can is thrown into the fire, what will the pressure when the temperature reaches 928 C

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