# chem chapter 5

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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
 Author: Anonymous ID: 45837 Card Set: chem chapter 5 Updated: 2010-10-29 04:28:39 Tags: review pt Folders: Description: october 28, 2010 Show Answers: