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What affects the behavior of a gas?

What affects the behavior of a gas?. The number of particles present Volume (the size of the container) Temperature. Behavior of gas??. Usually refers to pressure But what is pressure? Collisions between molecules & container More collisions = higher pressure. Number of particles.

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What affects the behavior of a gas?

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  1. What affects the behavior of a gas? • The number of particles present • Volume (the size of the container) • Temperature

  2. Behavior of gas?? • Usually refers to pressure • But what is pressure? • Collisions between molecules & container • More collisions = higher pressure

  3. Number of particles • Assume same volume & temperature… • Increasing the number of particles will increase the number of collisions • Increased collisions means increased pressure

  4. If you double the number of molecules 1 atm

  5. If you double the number of molecules • You double the pressure. 2 atm

  6. Number of particles • Decreasing the number of particles will decrease the number of collisions • Decreased collisions means decreased pressure

  7. 4 atm • As you remove molecules from a container

  8. 2 atm • As you remove molecules from a container the pressure decreases

  9. 1 atm • As you remove molecules from a container the pressure decreases • Until the pressure inside equals the pressure outside

  10. UNDERSTANDING CHECK

  11. Volume (the size of the container) • Assume constant number of particles & temperature • If the volume decreases, molecules have less room to move • More collisions = increased pressure

  12. 1 atm • As the volume of a gas decreases, 4 Liters

  13. As the volume of a gas decreases, the pressureincreases 2 atm 2 Liters

  14. Volume (size of the container) • If the volume increases, there is more room for the molecules to move • Fewer collisions = decreased pressure • SO… pressure and volume are INVERSELY related

  15. UNDERSTANDING CHECK

  16. Temperature • Assume volume and number of particles are constant • Raising the temperature of a gas makes the particles move faster • Faster movement = more collisions = increased pressure • Decreasing temp = slower movement = less collisions = decreased pressure • DIRECT relationship

  17. 300 K • Start with 1 liter of gas at 1 atm pressure and 300 K • Heat it to 600 K

  18. 600 K 300 K • Pressure will increase to 2 atm.

  19. 600 K 300 K (Start) • If volume not held constant, the volume will increase to 2 liters at 1 atm

  20. What does that mean? • Assume pressure is constant • Increasing the temperature will lead to an increase in volume • And thus decreasing the temperature will lead to a decrease in volume • Temperature & volume have a DIRECT relationship

  21. UNDERSTANDING CHECK

  22. Dalton’s Law of Partial Pressures • The total pressure inside a container is equal to the sum of the partial pressure of each gas. • The partial pressure of a gas is the pressure of that individual gas hitting the wall. • PTotal = P1 + P2 + P3 + … • For example

  23. We can find out the pressure in the fourth container • By adding up the pressure in the first 3 2 atm 1 atm 3 atm 6 atm

  24. Dalton’s Law • This means that we can treat gases in the same container as if they don’t affect each other. • We can figure out their pressures separately • And add them to get total pressure

  25. Pressure measurements • Can use 3 different units • Kilopascals (kPa) • Atmospheres (atm) • Millimeters of mercury (mm Hg) • Remember… • 1 atm = 101.3 kPa = 760 mm Hg

  26. Examples • What is the total pressure in a balloon filled with nitrogen & oxygen if the pressure of the oxygen is 170 mm Hg and the pressure of nitrogen is 620 mm Hg?

  27. Examples In a second balloon the total pressure is 1.3 atm. What is the pressure of oxygen if the pressure of nitrogen is 720 mm Hg?

  28. Gas Laws • To make things easier, we are going to assume the gases behave ideally • Assume particles have no volume • Assume no attractive forces between molecules • Situation does not really exist but it... • makes the math easier • close approximation to reality

  29. Boyle’s Law • At a constant temperature, pressure and volume are inversely related • As one goes up, the other goes down • P1V1 = P2V2

  30. P V

  31. Example • A balloon is filled with 25 L of air at 1.0 atm pressure. If the pressure is changed to 1.5 atm, what is the new volume?

  32. Example • A balloon is filled with 73 L of air at 1.3 atm pressure. What pressure is needed to change to a volume of 43 L?

  33. A sample of oxygen occupies 47.2 liters under a pressure of 1240 mm Hg at 25oC. What volume would it occupy at 25oC if the pressure were decreased to 730 mm Hg? (a) 27.8 L (b) 29.3 L (c) 32.3 L (d) 47.8 L (e) 80.2 L

  34. Charles’ Law • The volume of a gas is directly proportional to the Kelvin temperature if the pressure is held constant. • K = degrees Celsius + 273 • V1 = V2T1 T2

  35. V T

  36. Example • What is the temperature of a gas that is expanded from 2.5 L at 25ºC to 4.1L at constant pressure?

  37. Example • What is the final volume of a gas that starts at 8.3 L and 17ºC and is heated to 96ºC?

  38. A sample of nitrogen occupies 5.50 liters under a pressure of 900 mm Hg at 25oC. At what temperature will it occupy 10.0 liters at the same pressure? (a) 32oC (b) -109oC (c) 154oC (d) 269oC (e) 370oC

  39. Gay Lussac’s Law • The temperature and the pressure of a gas are directly related at constant volume. • P1 = P2T1 T2

  40. P T

  41. A rigid container at 25C has a pressure of 430 kPa. What would the pressure be at 125 C? A. 574 kPa B. 320 kPa C. 86 kPa D. 2200 kPa E. 620 kPa

  42. Examples • What is the pressure inside a 0.250 L can of deodorant that starts at 25ºC and 1.2 atm if the temperature is raised to 100ºC?

  43. Combined Gas Law • The Combined Gas Law deals with the situation where only the number of molecules stays constant. • Everything else varies • P1 V1 = P2 V2T1 T2 • Lets us figure out one thing when two of the others change.

  44. The combined gas law contains all the other gas laws! • If the temperature remains constant. P1 V1 P2 x V2 x = T1 T2 Boyle’s Law

  45. The combined gas law contains all the other gas laws! • If the pressure remains constant. P1 V1 P2 x V2 x = T1 T2 Charles’ Law

  46. The combined gas law contains all the other gas laws! • If the volume remains constant. P1 V1 P2 x V2 x = T1 T2 Gay-Lussac’s Law

  47. Examples • A 15 L cylinder of gas at 4.8 atm pressure at 25ºC is heated to 75ºC and compressed to 17 atm. What is the new volume?

  48. Examples • If 6.2 L of gas at 723 mm Hg at 21ºC is compressed to 2.2 L at 4117 mm Hg, what is the temperature of the gas?

  49. Adding another variable • Avogadro’s Hypothesis – If T & P constant, 2 equal volumes of gas contain the same # of molecules • 22.4 L = 1 mole = 6.022 x 1023 molecules • Volume has a DIRECT relationship to number of moles present • More volume = more moles • Add this to the combined gas law

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