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Gases…..

Gases…. Have neither shape nor volume Are highly compressible Diffuse ( move spontaneously throughout any available space until equally distributed ) Temperature affects either the volume or pressure of a gas or both. Pressure. is defined as a force per unit area

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Gases…..

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  1. Gases….. • Have neither shape nor volume • Are highly compressible • Diffuse (move spontaneously throughout any available space until equally distributed) • Temperature affects either the volume or pressure of a gas or both

  2. Pressure • is defined as a force per unit area • Since force can be measured in Newtons • And area can be measured in m2 • Then N/m2 is the unit which is the SI definition of a pascal • we measure pressure in kilopascal (kPa)

  3. Pressure • Atmospheric pressure is the force per unit area exerted by air on ALL objects

  4. STP 0 oC 101.325 kPa SATP – more convenient 25 0C 100kPa Standard conditions

  5. Other pressure units!!

  6. Effusion Manometer

  7. Boyle’s Law As pressure on a gas increases, the volume of the gas decreases proportionally, provided that that temperature and the chemical amount(moles) of gas remains constant So

  8. Boyle’s Law

  9. Temperature • is defined as the average kinetic energy of particles • We usually measure it in oC • but for gases we will use the absolute or Kelvintemperature scale • To convert from celsius simply add 273

  10. Charles’ Law As temperature of a gas increases, the volume of the gas increases proportionally, provided that that pressure and the chemical amount(moles) of gas remain constant

  11. Charles’ Law

  12. Combined Gas Law • Combination of Boyles and Charles’ Law and (Gay Lussac) • Unchanging conditions drop out of the equation • Remember temp MUST be in Kelvin 14

  13. Molar Volume • Molar volume is the volume that one mole of a gas occupies at a specified temperature and pressure….. • At STP 22.4 litres in one mole of a gas • At SATP 24.8 litres in one mole of a gas How do you convert between moles and volume?? How do you convert between mass and volume….one extra step!

  14. Example problem 1 • What is the volume of 0.24moles of CO2 (g)at STP??

  15. Example Problem 2 • What is the volume of 6.8g of Hydrogen gas at SATP??

  16. Perform the following conversions (all at SATP). • 1. 4.00 mol CH4(g) to L • 2. 2.25 mol NO(g) to L • 3. 4.275 g CO2(g) to L • 4. 1.27 g H2(g) to L • 5. 5.00 L O2(g) to mol O2(g) • 6. 3.50 L H2(g) to mol H2(g) • 7. 4.35 L CH4(g) to g CH4(g) • 8. 5.45 L N2(g) to g N2(g)

  17. Practice • Section questions #5-10 p. 171 • How can you get an egg in and out of a flask?????

  18. Ideal Gas Law

  19. What makes an “ideal gas” hypothetically??? • They obey ALL gas laws perfectly under ALL conditions • SO….they do not condense • ….graphs of v/T and p/T are straight lines • ….particle size is negligible with NO intermolecular attractions between them

  20. REAL gases are most ideal when • Pressure is ? • LOW • Because…..at high pressure molecules are forced together and their size becomes significant relative to the empty space in container • Temperature is ? • HIGH • Because…..at low temperature molecules are closer together, moving slower and thus experience intermolecular attraction (they condense)

  21. Therefore Simulation for Gas Laws

  22. Ideal Gas Law PV = nRT R is called the gas constant (combined gas law constants) R = 8.314 kPa.L mol.K Pressure MUST be in kPa and Volume in L and temp in Kelvin 24

  23. So many gas laws eh? 25

  24. Sample problem 4.4 Predict the volume of 0.78g of Hydrogen gas at 22°C and 125kPa Practice #3-5 p.175 and SQ #8,9,11, p. 176 26

  25. Explaining Gas Properties What is kinetic molecular theory??

  26. Kinetic molecular theory solid (vibrational) liquid (vibrational, rotational, and translational) gas (translational)

  27. Kinetic Molecular Theory 29

  28. Gas Pressure Pressure = total force applied to a certain area larger force = larger pressure smaller area = larger pressure • Gas pressure is caused by gas molecules colliding with the container or surface • More forceful collisions or more frequent collisions mean higher gas pressure 30

  29. Compressing a gas! 31

  30. Law of combining volumes • 1809….Joseph Gay-Lussac

  31. Law of combining volumes • 1811…Amedeo Avogadro e.g.

  32. Practice Questions #4-7, p.166 and p168 #1-5

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