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Understanding Gases: Properties, Behavior, and Key Laws

This chapter explores the fundamental properties of gases, highlighting their unique characteristics such as expansion, fluidity, low density, compressibility, and diffusion. It discusses essential gases such as oxygen, hydrogen, nitrogen, and carbon dioxide, along with their significance for life and environmental roles. The kinetic theory of gases is introduced, detailing particle motion and behavior in relation to temperature and pressure, followed by key gas laws, including Boyle's, Charles', and Gay-Lussac's laws that describe the relationships between pressure, volume, and temperature.

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Understanding Gases: Properties, Behavior, and Key Laws

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  1. Chapter 5 Gases

  2. Gas – neither definite shape or volume

  3. Oxygen • Joseph Priestley (1733 -1804)

  4. 21% of atmosphere • Necessary for life (respiration   photosynthesis)

  5. Combines with Si, Al, Fe, Ca, Mg, etc. to form rocks and minerals

  6. Lewis structure • Colorless, odorless, tasteless gas • reactive

  7. Supports combustion

  8. Ozone (O3) • Poisonous blue gas, pungent odor

  9. Hydrogen

  10. Most abundant element • Rocket fuel (liquid) • Possible fuel of the future

  11. Colorless, odorless, tasteless gas • reactive

  12. Nitrogen

  13. 78% of atmosphere • Non reactive • Important to life on earth • Nitrogen cycle

  14. Carbon Dioxide • Colorless gas • Important to life

  15. Tests for common gases

  16. Characteristics of Gases • Expansion • Fluidity

  17. (cont.) 3. Low density

  18. (cont.) • Compressibility • Diffusion

  19. Kinetic theory • Particles of matter are always in motion

  20. Ideal gas • Imaginary gas, conforms perfectly to kinetic theory • Kinetic theory applies only to an ideal gas, but many gases are close to ‘Ideal’

  21. Kinetic Theory of Gases • Gases consist of a lg. # of tiny particles, occupy a volume 1000x the volume of liquid or solid w/ the same # of particles • Constant motion • Elastic collisions of particles (no net loss of kinetic E)

  22. (cont.) • No forces of attraction or repulsion • Avg. KE is proportional to Kelvin temp. of gas

  23. 4 measurable quantities of gases • Volume (V) • Pressure (P) • Temperature (T, always in K) • # of molecules (moles)

  24. Temperature Scales • Absolute zero = -273.15oC (rounded to -273oC) = 0 K (not 0oK) • Therefore K = 273 + oC • 0 oC = 273 K

  25. Temp. conversions K = oC + 273 25.0 oC = ? K 273 + 25.0 = 298 = 298K

  26. Units of Pressure • Pressure at sea level & 0 oC =760 mmHg or 1 atm • Standard temperature and pressure (STP) = 1 atm & 0oC

  27. Convert a pressure of 0.830 atm to mmHg 0.830 atm x 760 mmHg/ 1 atm = 631 mmHg

  28. Write an equation for the relationship between P, V, and T (assume a constant # moles) P x V = a constant P/ T = a constant V/ T = a constant PV/ T = a constant P1V1/ T1 = P2V2/ T2

  29. Boyle’s Law • Volume off a fixed mass of gas varies inversely with pressure at a constant temperature

  30. Robert Boyle (1627-1691) • Born at Lismore Castle, Munster, Ireland, the 14th child of the Earl of Cork. • 1662, delineated the quantitative relationship that the volume of a gas varies inversely with pressure.

  31. Boyle’s Law • P1V1 = k and P2V2 = k • Therefore P1V1 = P2V2

  32. A sample of oxygen gas occupies a vol. of 150 mL at a pressure of 720 mmHg. What would the volume be at 750 mmHg press.? P1V1 = P2V2 or V2 = P1V1/ P2 = (720 mmHg)(150 mL)/ 750 mmHg = 144 mL = 140 mL oxygen gas

  33. France, early 1800’s • Hot air balloons were extremely popular • Scientists were eager to improve the performance of their balloons. Two of the prominent French scientists were Jacques Charles and Joseph-Louis Gay-Lussac,

  34. Charles’ Law • The volume of a fixed mass of gas varies directly with the Kelvin temperature at constant pressure Jacques Charles

  35. Charles’ Law • V1/ T1 = V2/ T2

  36. A sample of Ne gas has a vol. of 752 mL at 25.0 deg. C. What is the vol. at 50.0 deg. C? T1 = 25.0 deg. C = 298 K T2 = 50.0 deg C = 323 K V1 = 752 mL V1/ T1 = V2/ T2or V2 = V1T2/ T1 = 752 mL x 323 K/ 298K = 815 mL

  37. Gay-Lussac’s Law • The pressure of a fixed mass of gas varies directly with the Kelvin temp. at constant volume • P1/ T1 = P2/ T2

  38. P1/ T1 = P2/ T2

  39. A sample of N gas is at 3.00 atm of pressure at 25 deg C what would the pressure be at 52 deg C? P1 = 3.00 atm T1 = 25 deg C = 298 K T2 = 52 deg C = 325 K P2 = ? P1/ T1 = P2/ T2or P2 = P1T2/ T1

  40. (cont.) = (3.00 atm)(325 K)/ 298K = 3.27 atm = 3.3 atm

  41. Combined Gas Law • P1V1/ T1 = P2V2/ T2

  42. A helium filled balloon has a vol. of 50.0 L at 25 deg C and 820. mmHg of pressure. What would the vol. be at 650 mmHg pressure and 10. deg C? • P1V1/ T1 = P2V2/ T2 or V2 = P1V1T2/ P2T1 • V1 = 50.0 L • V2 = ? • T1 = 25 deg C = 298 K • T2 = 10. deg C = 283 K • P1 = 820. mmHg • P2 = 650 mmHg

  43. (cont) V2 = (820. mmHg)(50.0 L)(283K)/ (650. mmHg)(298 K) =59.9 L = 60. L

  44. Molar Volume of a Gas • One mole of gas (6.02 x 1023 molecules) has the same volume at STP (0 deg C, 1 atm) as any other gas

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