Transcript I. Physical Properties of Gases

Gases
I. Physical
Properties
Ch 12.1 & 13
Kinetic Molecular Theory
1.
2.
3.
4.
5.
Particles of matter are ALWAYS in
motion
Volume of individual particles is 
zero.
Collisions of particles with container
walls cause pressure exerted by gas.
Particles exert no forces on each
other.
Average kinetic energy is
proportional to Kelvin temperature of
a gas.
A. Ideal Gases
Ideal gases are imaginary gases that perfectly
fit all of the assumptions of the kinetic molecular
theory.
Gases consist of tiny particles that are far
apart relative to their size.
Gas particles have elastic collisions
No kinetic energy is lost in elastic
collisions
Gas particles are in constant motion.
There are no attractive forces between gas
particles
The average kinetic energy of gas particles
depends on temperature, not on the identity
of the particle.
B. 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 Gases
 Gases
expand to fill any container.
 Gases
are fluid like.
 Gases
have very low densities.
C. Characteristics of Gases
 Gases
can be compressed.
• lots of empty space
 Gases
undergo diffusion & effusion.
• random motion
C. Characteristics of Gases
 Graham’s
Law
 Diffusion
• Spreading of gas molecules
throughout a container until
evenly distributed.
 Effusion
• Passing of gas molecules
through a tiny opening in a
container
C. Characteristics of Gases
 Speed
of diffusion/effusion
• Kinetic energy is determined by
the temperature of the gas.
• At the same temp & KE, heavier
molecules move more slowly.
 Larger m  smaller v
KE =
2
½mv
D. Temperature
 Always
use absolute temperature
(Kelvin) when working with gases.
ºF
-459
ºC
-273
K
0
32
212
0
100
273
373
E. Pressure
force
pressure 
area
Which shoes create the most pressure?
E. Pressure
 Barometer
• measures atmospheric pressure
Aneroid Barometer
Mercury Barometer
E. Pressure
 Manometer
• measures contained gas pressure
U-tube Manometer
Bourdon-tube gauge
E. Pressure
 KEY
UNITS AT SEA LEVEL
101.325 kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
N
Pa  2
m
F. STP
STP
Standard Temperature & Pressure
0°C
273 K
-OR-
1 atm
101.325 kPa