chem chapter 5

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Anonymous
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45837
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chem chapter 5
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2010-10-29 00:28:39
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october 28, 2010
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  1. characteristics of gases
    • made up of all nonmetals
    • low MW compounds
    • expand to fill a container
    • gases are compressible
    • gases mix homogeneously when combined
  2. vapor
    gas of a compound that is liquid at the given temperature
  3. why does a balloon expand when you blow into it?
    increase in pressure because of more gas molecs colliding with the walls
  4. atmosphere
    • gases in atmosphere are "pulled" toward earth by gravity --- causing pressure
    • how is it measured?
    • barometer
    • usually measured in atm
  5. barometer
    how atmosphere is measured
  6. 1 atm
    • standard atmospheric pressure
    • enough pressure to push mercury(Hg) column to a height of 760mmHg = 760 torr

    1atm = 760mmHg = 760 torr
  7. how is pressure in a closed system measured?
    manometer
  8. open-ended column
    • *units have to be the same for Pgas & Patm
    • delta(h) = difference in heights

    if column heights are equal: Pgas = Patm

    if Patm > Pgas Pgas = Patm - delta(h)

    if Patm < Pgas Pgas = Patm + delta(h)
  9. closed manometer
    • *atmospheric pressure does not matter
    • vacuum is on "open" end
    • vacuum:
    • absence of any molecs
    • 0 pressure
    • Gas must push harder than vacuum to have pressure
    • Pgas = delta(h)
  10. four variables with gases
    • T = temp, must be in Kelvin(K)
    • P = pressure
    • V = volume
    • n = # of moles of gas present
    • (never a gram relationship)
  11. ideal gas law
    PV=nRT

    R, ideal gas constant...use block!! or 0.08206L*atm/mol*K

    • 22.4L*1atm
    • 1mol*273K

    1atm = 760mmHg(or torr) = 101.3kpa
  12. relate V and P
    • P1V1 = P2V2
    • V goes up, P goes down
  13. relate V and T
    • V1/T1 = V2/T2
    • V goes up, P goes up
  14. relate V and n
    • V1/n1 = V2/n2
    • V goes up, n goes up
  15. facts
    • while the MW of gases can vary significally, the volume depends only on the number of particles of gas present (moles)
    • weights vary (because of MW), but at STP, 1 mole of gas will always have the same volume.
  16. ideal gas definition
    hypothetical gas that behaves according to the ideal gas law (PV= nRT)
  17. density
    mass per unit volume (mass/volume)

    • dgases = g/L
    • dliquids = g/mL

    OR

    d = P(MW)/ RT
  18. rearrange density equation to equal MW
    • original:
    • d = P(MW)/RT

    • rearranged:
    • MW = dRT/P
  19. more than one gas present:
    • each gas acts like it's alone
    • identity of molecs of gas is not important
  20. dalton's law of partial pressures
    the total pressure of a mixture of gases is the sum of the partial pressure of gases in the mixture

    P = nRT/V

    *pressure depends on the number of molecules/atoms or moles of gas present
  21. kinetic molecular theory
    a way to visualize what the molecules are doing

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