physical properties ch. 10 & 11 - gases. a. kinetic molecular theory b particles in an ideal...
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Physical PropertiesPhysical
Properties
Ch. 10 & 11 - Ch. 10 & 11 - GasesGases
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A. Kinetic Molecular A. Kinetic Molecular TheoryTheoryA. Kinetic Molecular A. Kinetic Molecular TheoryTheory
Particles in an ideal gas…• have no volume.• have elastic collisions. • are in constant, random, straight-
line motion.• don’t attract or repel each other.• have an avg. KE directly related to
Kelvin temperature.
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Ideal Gases donIdeal Gases don’’t existt existIdeal Gases donIdeal Gases don’’t existt exist
Molecules do take up space
• All matter has volumeThere are attractive forces
• otherwise there would be no liquids
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Ideal GasesIdeal GasesIdeal GasesIdeal Gases
There are no gases for which this is true.
Real gases behave this way at high temperature and low pressure.
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Ideal GasesIdeal GasesIdeal GasesIdeal Gases
In this chapter we are going to assume the gases behave ideally
Does not really exist • makes the math easier • close approximation.
Assume particles have no volumeAssume no attractive forces
between molecules
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B. Real GasesB. Real GasesB. Real GasesB. Real Gases
Particles in a REAL gas…
• have their own volume
• attract each other
Gas behavior is most ideal…
• at low pressures
• at high temperatures
• in nonpolar atoms/molecules
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Real Gases behave like Real Gases behave like Ideal GasesIdeal GasesReal Gases behave like Real Gases behave like Ideal GasesIdeal Gases
When the molecules are far apart
They take a smaller percentage of the space
Ignoring their volume is reasonable
This is at low pressure
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Real Gases behave like Real Gases behave like Ideal gases whenIdeal gases whenReal Gases behave like Real Gases behave like Ideal gases whenIdeal gases when
Molecules are moving fast.Molecules are not next to each
other very longAttractive forces can’t play a role.At high temp.Far above boiling point.
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C. Johannesson
C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesGases expand to fill any container.
• random motion, no attraction
Gases are fluids (like liquids).• no attraction
Gases have very low densities.• no volume = lots of empty space
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C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesGases can be compressed.
• no volume = lots of empty space
Gases undergo diffusion & effusion.• random motion
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DiffusionDiffusionDiffusionDiffusion
Molecules moving from areas of high concentration to low concentration.
Perfume molecules spreading across the room.
Effusion - Gas escaping through a tiny hole in a container.
From high to low concentration Both depend on the speed of the
molecules
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C. Johannesson
D. TemperatureD. TemperatureD. TemperatureD. Temperature
ºF
ºC
K
-459 32 212
-273 0 100
0 273 373
K = ºC + 273
Always use absolute temperature (Kelvin) when working with gases.
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E. PressureE. PressureE. PressureE. Pressure
area
forcepressure
Which shoes create the most pressure?
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E. PressureE. PressureE. PressureE. Pressure
Barometer• measures atmospheric pressure
Mercury Barometer
Aneroid Barometer
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E. PressureE. PressureE. PressureE. Pressure
Manometer• measures contained gas pressure
U-tube Manometer Bourdon-tube gauge
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E. PressureE. PressureE. PressureE. Pressure
2m
NkPa
KEY UNITS AT SEA LEVEL
101.325 kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
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F. STPF. STPF. STPF. STP
Standard Temperature & PressureStandard Temperature & Pressure
0°C 273 K
1 atm 101.325 kPa-OR-
STP