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I. Physical PropertiesI. Physical Properties
12.1- Gases12.1- Gases
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A. Kinetic Molecular A. Kinetic Molecular TheoryTheoryA. Kinetic Molecular A. Kinetic Molecular TheoryTheory
kinetic-molecular theory: (def) theory of the energy of particles and the forces that act between them; based on idea that particles of matter are always in motion
Kinetic molecular theory describes the motion of an ideal gas
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A. Kinetic Molecular A. Kinetic Molecular TheoryTheoryA. Kinetic Molecular A. Kinetic Molecular TheoryTheory
ideal gas: (def) imaginary gas that perfectly fits the assumptions of the kinetic-molecular theory
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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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B. Real GasesB. Real GasesB. Real GasesB. Real Gases
Particles in a REAL gas…• have their own volume• attract each other• proposed by van der Waals
Gas behavior is most ideal…• at low pressures• at high temperatures• in nonpolar atoms/molecules
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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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C. Characteristics of C. Characteristics of GasesGasesC. Characteristics of C. Characteristics of GasesGasesDiffusion: (def) process by which gases spontaneously spread out and mix with
other gases; lighter gases diffuse more quickly
Effusion: (def) process by which gases particles under pressure pass through a tiny opening; lighter gases effuse faster
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A. TemperatureA. TemperatureA. TemperatureA. Temperature
ºF
ºC
K
-459 32 212
-273 0 100
0 273 373
32FC 95 K = ºC + 273.15
Always use absolute temperature (Kelvin) when working with gases.
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B. PressureB. PressureB. PressureB. Pressure
area
forcepressure
Which shoes create the most pressure?
SI unit of force is the Newton
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. Pressure. Pressure. Pressure. Pressure Barometer
• measures atmospheric pressure - at sea level,
height of column is
760 mm
- P of Hg is equal to the P of the atmosphere
Mercury Barometer
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E. PressureE. PressureE. PressureE. Pressure
Manometer• measures contained gas pressure
- difference in height of tubes indicates the
gas pressure
U-tube Manometer
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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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Pressure Pressure Pressure Pressure Unit Symbol Definitions
Pascal Pa SI Pressure Unit;
1 Pa = 1 N/m2
Millimeter of
Mercury
mm Hg P that supports a 1 mm mercury column in a barometer
Atmo-sphere
atm 1 atm = 760 mm Hg
= 101.325 kPa
Torr torr 1 torr = 1 mm Hg
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C. STPC. STPC. STPC. STP
Standard Temperature & PressureStandard Temperature & Pressure
0°C 273.15 K
1 atm 101.325 kPa-OR-
STP
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D. Dalton’s lawD. Dalton’s lawD. Dalton’s lawD. Dalton’s law
Dalton’s law of partial pressure:
• Ptotal = P1 + P2 + P3…+Pn
(n = number of gases in mixture)
**Total P exerted by collection gases is sum of pressure exerted by each gas