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Chapter 5

Chapter 5. Gases. Gas – neither definite shape or volume. Oxygen. Joseph Priestley (1733 -1804). 21% of atmosphere Necessary for life (respiration   photosynthesis). Combines with Si, Al, Fe, Ca, Mg, etc. to form rocks and minerals. Lewis structure

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Chapter 5

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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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