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October 28

October 28. AIM: What are the general properties of gases and what is PRESSURE ? Atmospheric pressure Units Gas pressure. Gases. Gases fill completely the container they are in (INDEFINITE VOLUME). Gases assume the shape of the container they are in (INDEFINITE SHAPE).

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October 28

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  1. October 28 AIM: What are the general properties of gases and what is PRESSURE ? Atmospheric pressure Units Gas pressure

  2. Gases • Gases fill completely the container they are in (INDEFINITE VOLUME). • Gases assume the shape of the container they are in (INDEFINITE SHAPE). • Gas particles are separated from each other and move fast. • Gases are fluids, have low densities and are highly compressible.

  3. Air Pressure or Atmospheric pressure Is the force that the atmosphere exerts over the surface of the Earth. It depends on the weather. It changes with altitude. It is measured with a BAROMETER.

  4. Atmospheric pressure is the weight of air per unit of area.

  5. Barometer Evangelista Torricelli made the first barometer in 1644

  6. UNITS FOR PRESSURE ATMOSPHERE = atm Torricelli = torr Millimiters of Mercury = mm of Hg KiloPascal = kPa

  7. Normal Atmospheric Pressure (the pressure at sea level) 1 atm = 101.3 kPa = 760 mm of Hg

  8. STP - STANDARD TEMPERATURE AND PRESSURE Table A 0 0 C or 273 K 1 atm=101.3 kPa=760 mm of Hg=760 torr

  9. Gas pressure Gas particles are in continuous motion. Gases exert pressure by colliding with the walls of the container they are in. The force exerted over the area of the wall is the pressure of the gas. The greater the number of gas particles in a container the greater the pressure.

  10. Collision against the walls of the container exert pressure

  11. Gases Have indefinite shape and indefinite volume. Gases will assume the shape and volume of the container the are in. The particles inside a gas are in constant motion. Gas particles exert pressure against the walls of the container

  12. October 29 • BOYLE’S LAW • Relationship between pressure and volume for a gas

  13. Boyle’s Law (1644) The volume of a fixed quantity of gas at constant temperature is inversely proportional to the pressure. WHEN PRESSURE INCREASES THE VOLUME DECREASES (AT CONSTANT TEMPERATURE)

  14. As P and V areinversely proportional A plot of V versus P results in a curve at constant T PV = k

  15. EQUATION FOR BOYLE’S LAW PROBLEMS • P1 X V1 = P2 X V2 AT CONSTANT T INITIAL FINAL

  16. October 29 • Review of Boyle’s Law problems • Relationship between temperature and volume of a gas at constant pressure- Charles’ Law • TEST ON GASES WEDNESDAY NOV 21

  17. Answers to Boyle’s Law Worksheet • 1. 9.38 L • 2. 3L • 3. B • 4. C • 5. C • 6. C • 7. C • 9. 2.0 • 10. 200 mL

  18. Boyle’s Law Worksheet • 1. 1atm = 101.3 kPa • 2. P2= 607.8 kPa • 3. V2 = 300 L • 4 V2 = 27 L • 5 Decreases • Textbook page 415 • Gases ch 12 • Up to 428 review for • monday

  19. Jacques Charles-Charles’ Law - 1802

  20. Charles’s Law The volume of a fixed amount of gas at constant pressure is directly proportional to its absolute temperature. V T = k A plot of V versus T will be a straight line.

  21. EQUATION FOR CHARLES’ LAW PROBLEMS • T1 / V1 = T2 / V2 AT CONSTANT P INITIAL FINAL REMEMBER THAT TEMPERATURE MUST BE IN K

  22. DO NOW: What is the final volume of 20 mL of a gas at STP if it is heated up to 546 K at constant Pressure? SET IT UP AND SHOW YOUR WORK

  23. Problems with Charles’ Law • TEMPERATURE MUST BE IN K! • Pressure is constant

  24. Charles’ Law answers • 1. 146.5 K • 2. 682 mL • 3. 1215 mL • 4. 54.5 mL • 5. 293 mL • 6. 2.2 mL • 7. 8.5 L • 8. 321mL • 9. 4.14 L • 10. 4.14 L • 11. 7 L • 12. 615 mL • 13. 410 mL • 14. 67.7 mL • 15. 29 mL • 16. decreases • 17 . 2

  25. THIRD LAW- RELATIONSHIP BETWEEN P AND T AT CONSTANT V • The pressure of a gas at constant volume is directly proportional to its K temperature

  26. Review gas laws • The combined gas law

  27. DO NOW QUIZ! The temperature of 4.0 L of a gas is changed from 40 C to 0 C at constant pressure. Find the new volume. SET UP AND SOLVE REMEMBER EACH STEP IS ONE POINT!

  28. COMBINED GAS LAW • When no variable is kept constant. FORMULA IN TABLE T V1 = V2 = T1 = T2 = P1 = P2 =

  29. Kinetic Theory of Gases • Ideal vs Real gases • Deviation from ideal behavior

  30. Kinetic theory of gases (under ideal circumstances) Gas are composed of particles that are in constant, rapid, random, linear motion. Collisions between gas particles are elastic so no energy is lost. As a result, the pressure of a gas at a constant temperature and volume remains constant The volume of the particles of a gas is so small compared to the distance between them, it is considered zero. The gas is mostly space. There is no attraction or repulsion between gas molecules The average kinetic energy of the molecules of a gas is directly proportional to the Kelvin temperature of the gas

  31. Deviation : noticeable or marked departure from accepted norms of behavior • Random : without definite aim, direction, rule, or method

  32. Ideal Gas • Motion - at random • Collision – cause pressure • Volume – insignificant • Attraction – no attractions

  33. Deviations from ideal behavior Particles of gas do have volume Gas particles do attract each other Optimum conditions High temperature Low pressure Low molecular mass ( H2 and He are the lightest gases )

  34. Real Gases • Motion - at random • Collision – cause pressure • Volume – can become significant • Attraction –weak attraction- but do exist

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