I. Physical PropertiesI. Physical Properties
12.1- Gases12.1- Gases
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
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
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.
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
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
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
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.
B. PressureB. PressureB. PressureB. Pressure
area
forcepressure
Which shoes create the most pressure?
SI unit of force is the Newton
. 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
E. PressureE. PressureE. PressureE. Pressure
Manometer• measures contained gas pressure
- difference in height of tubes indicates the
gas pressure
U-tube Manometer
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
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
C. STPC. STPC. STPC. STP
Standard Temperature & PressureStandard Temperature & Pressure
0°C 273.15 K
1 atm 101.325 kPa-OR-
STP
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