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III. Physical Properties
Ch. 13 - GasesCh. 13 - Gases
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
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
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
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
State Changes
D. Describing GasesD. Describing GasesD. Describing GasesD. Describing Gases
Gases can be described by their:
• Temperature
• Pressure
• Volume
• Number of molecules/moles
• K
• atm
• L
• #
E. TemperatureE. TemperatureE. TemperatureE. Temperature
ºF
ºC
K
-459 32 212
-273 0 100
0 273 373
32FC 95 K = ºC + 273
Always use absolute temperature (Kelvin) when working with gases!
F. PressureF. PressureF. PressureF. Pressure
area
forcepressure
Which shoes create the most pressure?
F. PressureF. PressureF. PressureF. Pressure
Barometer• measures atmospheric pressure
exact height of the Hg depends on atmospheric pressure
usually measured in mm Hg
F. PressureF. PressureF. PressureF. Pressure
Manometer• measures contained gas pressure
Difference in height in two arms of U-tube is measure of pressure of gas sample
measured in various different units
F. PressureF. PressureF. PressureF. Pressure
2m
NPa
KEY EQUIVALENT UNITS
101.325 kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
G. STPG. STPG. STPG. STP
Standard Temperature & PressureStandard Temperature & Pressure
0°C 273 K
1 atm 101.325 kPa-OR-
STP
H. Pressure Problem 1H. Pressure Problem 1H. Pressure Problem 1H. Pressure Problem 1
The average pressure in Denver, Colorado, is 0.830 atm. Express this in (a) mm Hg and (b) kPa.
(a) 0.830 atm
1 atm
760 mm Hg= 631
mm Hg
(b) 0.830 atm
1 atm
101.325 kPa= 84.1
kPa
H. Pressure Problem 2H. Pressure Problem 2H. Pressure Problem 2H. Pressure Problem 2
Convert a pressure of 1.75 atm to kPa and mm Hg.
(a) 1.75 atm
1 atm
101.325 kPa= 177
kPa
(b) 1.75 atm
1 atm
760 mm Hg= 1330
mm Hg
H. Pressure Problem 3H. Pressure Problem 3H. Pressure Problem 3H. Pressure Problem 3
Convert a pressure of 570. torr to atmospheres and kPa.
(a) 570 torr
760 torr
1 atm= .750
atm
(b) 570 torr
760 torr
101.325 kPa= 76.0
kPa