CLE 3221.2.3 Apply the kinetic molecular theory to describe solids, liquids,
and gases.
CLE 3321.2.4 Investigate characteristics associated with the gaseous state.
SPI 3221.2.6 Investigate similarities and differences among solids, liquids
and gases in terms of energy and particle spacing.
SPI 3221.2.7 Predict how changes in volume, temperature, and pressure
affect the behavior of a gas.
CLE 3221.3.3 Explore the mathematics of chemical formulas and equations.
SPI 3221.3.5 Convert among the following quantities of a substance: mass,
number of moles, number of particles, molar volume at STP
Up, Up and Away
with Gases
Kinetic Molecular Theory
(KMT)
used to describe
behavior of gases,
liquids and solids
• all matter is composed
of small particles
(molecules)
• particles are in constant
motion (kinetic energy –
energy of motion)
• collisions between
particles are elastic
(no loss of KE)
gas
solid
liquid
Gas
weak attractive
forces between
particles, so
particles spaced far apart
relative to their size
frequent collisions due to
constant, random motion
We will use the KMT to
look at the following
characteristics of gases:
• volume
• temperature
• pressure
Volume
amount of space an
object occupies
gas particles expand to
fill volume of container
because of distance
between particles gases
can easily be compressed
Gases are “springy”
Temperature
related to the average
kinetic energy of
particles
Temperature scales
Celsius scale
based on freezing and
boiling points of water
o
o
(0 C – 100 C)
Kelvin scale
based on absolute zero
(0 K) temperature at
which particles are at
lowest possible energy
no negative numbers
K = oC + 273
oC
= K – 273
Temperature conversions
a. 110 oC to K
b. 303 K to
oC
c. -2.45 oC to K
Pressure
force exerted over
an area
Gas particles exert
pressure when they collide
with sides of container.
Atmosphere forms an
ocean of air above us.
Barometer
device used to measure
atmospheric pressure
Pressure units:
millimeters of mercury
(mm Hg) / torr
pounds per square inch
(psi)
atmospheres (atm)
kilopascals (kPa)
In order to compare two
different gas samples,
scientist define standard
conditions.
Compare apples to apples,
not apples to oranges!
Standard Temperature
and Pressure (STP)
0
oC
273 K
760 mm Hg (torr),
14.7 psi, 1.00 atm,
101.3 kPa
(atmospheric pressure at
sea level)
In marked contrast to solids
and liquids, gas volumes
change noticeably with
small changes in pressure
and temperature.
Gas laws
simple mathematical
relationships between
the volume, temperature,
pressure, and amount of
a gas
Ideal gas
particles have mass
but no volume; no
attractive forces
between particles
Most gases behave as
ideal gases except under
the conditions of:
1) very high pressure
2) very low temperature
Robert Boyle
Boyle’s Law
(volume and pressure)
The volume of a fixed
amount of gas held at a
constant temperature
varies inversely with the
pressure.
P1V1 = P2V2
Every breath I take . . .
As the diaphragm contracts
and flattens, chest cavity
enlarges. Volume increases
and pressure decreases
(Boyle’s law.) This creates
a vacuum, which pulls air
into the lungs. Note:
temperature is not kept
completely constant.
Oxygen is collected in
a 5.00 L glass bulb at a
pressure of 740 mmHg.
It is then pumped into
an evacuated container
having a volume of 1.50 L.
What is the pressure of
the gas?
Answer: 2 500 mmHg
An air-filled balloon has a
volume of 0.500 L at sea
level (standard pressure.)
What is the volume of the
balloon at the top of a
mountain where
atmospheric pressure is
745 mm Hg?
Answer: 0.510 L
Jacques Charles
French scientist
early balloonist
Charles’s Law
(volume and temperature)
The volume of a given
amount of gas is directly
proportional to its kelvin
temperature at constant
pressure.
As air inside balloon is
heated, volume increases
(Charles’s law.) Keep
heating and some air spills
out the bottom. Less air
inside makes balloon
lighter and lifts off ground.
A sample of hydrogen
gas occupies a volume
of 125 mL at 300. K.
Predict its volume at
standard temperature.
Answer: 114 mL
A sample of air in a piston
at 25 oC occupies 35 mL.
What volume will it occupy
if the temperature is raised
o
to 250 C?
Hint: Watch temperature
units!
Answer: 61 mL
A gas occupies a
volume of 562 mL at a
o
temperature of 120.1 C.
To what temperature,
in 0C, must the gas be
lowered, if it is to
occupy 400.0 mL?
Answer: 7 oC
Joseph Louis Gay-Lussac
French
chemist and
physicist
Gay-Lussac’s Law:
(pressure and temperature)
The pressure of a fixed
amount of gas varies
directly with the kelvin
temperature when the
volume remains constant.
Before a trip from New York
to Boston, the pressure in
an automobile tire is 1.8 atm
at 20. oC. At the end of the
trip, the pressure gauge
reads 1.9 atm. What is the
new Celsius temperature of
the air inside the tire?
Answer: 36
oC
At 120. oC, the pressure
of a sample of nitrogen is
1.07 atm. What will the
pressure be at 205 oC?
Answer:
1.30 atm
Combined Gas Law
states the relationship
among pressure,
temperature, and volume
of a fixed amount of gas
The volume of a gas is
27.5 mL at 22.0 oC and
0.974 atm.
What will the volume be
at 15.0 oC and 0.993 atm?
Answer: 26.3 mL
A student collects 450. mL
of hydrogen chloride gas
o
at 750. mm Hg and 17 C.
What is the volume of the
gas at STP?
Answer: 418 mL
A 700. mL gas sample at
STP is compressed to a
volume of 200. mL, and the
temperature is increased
o
to 30.0 C. What is the
new pressure of the gas in
kilopascals?
Answer 394 kPa
Avogadro’s principle
Equal volume of gases
at the same temperature
and pressure contain
equal numbers
of particles.
Molar volume
One mole of any gas at
STP occupies a volume
of 22.4 L
1 mol = 22.4 L
How many moles of
acetylene (C2H2) gas
occupy a volume of
3.25 L at STP?
Answer: 0.145 mol C2H2
What volume will 3.20 mol
of oxygen gas occupy at
STP?
Answer: 71.7 L O2
What is the volume of
7.17 g of neon gas at STP?
Answer: 7.96 L Ne
What is the volume of
5.0 g of hydrogen gas at
STP?
Answer: 56 L H2
The following websites were
accessed for this
presentation:
http://health.allrefer.com/pict
ures-images/diaphragm-andlungs.html
http://van.physics.illinois.edu/
qa/listing.php?id=2122
http://www.grc.nasa.gov/WW
W/K-12/airplane/kinth.html