Transcript The Gas Laws

The Gas Laws
The density of a gas decreases as its temperature increases.
Chemical Properties Produce
Gases
• Chemists harness
chemical properties to
produce a desired gas
through chemical
reactions. Such as the
reaction of zinc and
hydrochloric acid.
Physical Properties of Gases
Gases are compressible and that they
assume the shape and volume of any
container. Gases are all infinitely
soluble in one another. Each of these
characteristics can be explained by the
distances between the molecules (or
atoms) in a gaseous sample.
Physical Properties of Gases are
affected by temperature and pressure
States of matter simulation.
Collisions of Gas Particles
Kinetic Molecular Theory
 explains why gases behave as they do
 deals with “ideal” gas particles…
Kinetic Theory
Kinetic Molecular Theory
Postulates of the Kinetic Molecular Theory of Gases
1. Gases consist of tiny particles (atoms or molecules)
2. These particles are so small, compared with the distances
between them, that the volume (size) of the individual particles
can be assumed to be negligible (zero).
3. The particles are in constant random motion, colliding with the
walls of the container. These collisions with the walls cause the
pressure exerted by the gas.
4. The particles are assumed not to attract or to repel each other.
5. The average kinetic energy of the gas particles is directly
proportional to the Kelvin temperature of the gas.
Kinetic Molecular Theory
Evidence
Postulates
1. Gases are tiny molecules in mostly
empty space.
The compressibility of gases.
2. There are no attractive forces
between molecules.
Gases do not clump.
3. The molecules move in constant,
rapid, random, straight-line motion.
Gases mix rapidly.
4. The molecules collide classically
with container walls and one another.
Gases exert pressure that
does not diminish over time.
5. The average kinetic energy of the
molecules is proportional to the Kelvin
temperature of the sample.
Charles’ Law
Newton’s First Law of Motion (Law of Inertia)
Object at rest tends to
stay at rest, and object in
motion tends to stay in
motion at constant
velocity unless object is
acted upon by an
unbalanced, external
force.
inertia  mass
Elastic vs. Inelastic Collisions
8
3
Elastic vs. Inelastic Collisions
v1
POW
v2
8
elastic collision
v3
v4
8
inelastic collision
Elastic Collision
v1
8
before
8
after
v2
Model Gas Behavior
• All collisions must be elastic
• Take one step per beat of the
metronome
• Container
– Class stands outside tape box


• Higher temperature
– Faster beats of metronome
• Decreased volume
– Divide box in half
• More Moles
– More students are inside box





Mark area of container
with tape on ground.
Add only a few molecules
of inert gas
Increase temperature
Decrease volume
Add more gas
Effect of diffusion
Effect of effusion
(opening size)
Kinetic Molecular Theory
• 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.
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
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
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Characteristics of Gases
Gases 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
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Characteristics of Gases
• Gases can be compressed.
– no volume = lots of empty space
• Gases undergo diffusion & effusion.
– random motion
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Pressure
• Pressure is defined as
force divided by the
area.
F
P
A
Pressure
• The mercury in the inverted tube is
pushed upward by the force of
atmospheric pressure pushing down on
the surface of the mercury in the dish.
The height of the mercury in the tube
changes with changing atmospheric
pressure. Under conditions of standard
atmospheric pressure, the height of the
mercury in the tube is 760 mm. (1 atm =
760 mm Hg = 760 torr = 1.01325 kPa)
Collisions cause Pressure
• The pressure of a gas is
caused by the collision of
molecules against the
sides of the container.
The force of the collision
against the container can
be calculated by
Newton’s Second Law of
Motion: F=ma. The “F”
= force, “m”=mass in kg
and “a” is the
acceleration in m/s2.
Low Pressure vs. High Pressure
inside a System
The number of collisions
of gas molecules against
the wall of the container
determines the pressure
in the container. Notice
the difference in the
number of collisions.
Figure (a) would have a
lower pressure than
Figure (b).
Pressure
Is caused by the collisions of molecules with
the walls of a container
is equal to force/unit area
SI units = Newton/meter2 = 1 Pascal (Pa)
1 standard atmosphere = 101,325 Pa
1 standard atmosphere = 1 atm =
760 mm Hg = 760 torr
Pressure
KEY UNITS AT SEA LEVEL
101.325 kPa (kilopascal)
1 atm
760 mm Hg
760 torr
14.7 psi
N
kPa  2
m
1 bar = 100 kPa
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem
Sea level
Measuring Pressure
The first device for measuring
atmospheric
pressure was developed by
Evangelista Torricelli
during the 17th century.
The device was called a “barometer”
Baro = weight
Meter = measure
“We live submerged at the
bottom of an ocean of air.”
Evangelista Torricelli, circa 1644
Barometer
Empty space
(a vacuum)
Hg
Weight of the
mercury in
the column
Weight of the
atmosphere
(atmospheric
pressure)
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 401
Water column
Barometer
(34.0 ft. high
or 10.4 m)
• Mercury filled
760 mm = 1 atm
Atmospheric
pressure
• Water filled
10400 mm = 1 atm
Mercury column
(30.0 in. high
or 76 cm)
The barometer measures
air pressure
fraction
of 1 atm
average altitude
(m)
1
(ft)
0
0
1/2
5,486
18,000
1/3
8,376
27,480
1/10
16,132
52,926
1/100
30,901
101,381
1/1000
48,467
159,013
1/10000
69,464
227,899
1/100000
96,282
283,076
Sea level
Barometers
Mount Everest
Sea level
On top of Mount Everest
Pressure Practice
Convert the
following:
1. 145 mm Hg into
bars
2. 450 psi into kPa
3. 900 mm Hg into
torrs
4. 4580 Pa into kPa
5. 25 psi into atm
6. 150 atm into Pa
7. 109 kPa into atm
8. 76.9 mm Hg into
bars
9. 98.6 torr into kPa
10. 3 atm into kPa
Answers
1)
2)
3)
4)
5)
6)
0.19 bars
3102.4 kPa
900 torr
4.58 kPa
1.7 at5m
15199108.32 Pa
7) 0.10 bars
8) 13.14 kPa
9) 303.98 kPa
10) 1.08 atm
Temperature
Always use absolute temperature (Kelvin)
when working with gases.
ºF
-459
ºC
-273
K
0
C  F  32
5
9
32
212
0
100
273
373
K = ºC + 273
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STP
STP
Standard Temperature & Pressure
273 K
0°C
1 atm
- OR -
101.325 kPa
760 mm Hg
Courtesy Christy Johannesson www.nisd.net/communicationsarts/pages/chem