The Behavior of Gases
The word kinetic refers to motion
The energy an object has because of its motion is
called kinetic energy.
According to the kinetic theory, all matter consists
of tiny particles that are in constant motion.
The particles in a gas are usually molecules or
atoms.
The Behavior of Gases
The kinetic theory as it applies to gases includes the
following fundamental assumptions about gases:
1. The particles in a gas are considered to be
small, hard spheres with an insignificant volume.
Within a gas, the particles are relatively far apart
compared with the distance between particles in a liquid
or solid.
Between the particles, there is empty space.
No attractive or repulsive forces exist between the
particles.
The Behavior of Gases
The kinetic theory as it applies to gases includes the
following fundamental assumptions about gases:
2. The motion of particles in a gas is rapid,
constant, and random. Gases fill their containers regardless of the shape and volume
of the containers.
An uncontained gas can spread out into space without limit.
The particles travel in straight-line paths until they collide with
another particle and then change direction only when they
rebound from collisions.
The Behavior of Gases
The kinetic theory as it applies to gases
includes the following fundamental
assumptions about gases:
3. All collisions between particles in a gas are
perfectly elastic.
During an elastic collision, kinetic energy is transferred
without loss from one particle to another.
The total kinetic energy remains constant.
The Behavior of Gases
Gases are easily compressed, or squeezed
into a smaller volume.
Compressibility is a measure of how much the
volume of matter decreases under pressure.
Gases are easily compressed because of the
space between the particles in a gas.
The Behavior of Gases
This model shows identical air samples in two
different containers. Each container has 8
nitrogen molecules and 2 oxygen molecules.
In the larger container,
the molecules are
farther apart.
In the smaller container,
the air sample is
compressed, and the
molecules are closer
together.
The Behavior of Gases
Gas pressure results from the force exerted
by a gas per unit surface area of an object.
Gas pressure is the result of billions of rapidly
moving particles in a gas simultaneously
colliding with an object
If no particles are present, no collisions can occur.
Consequently, there is no pressure.
An empty space with no particles and no pressure
is called a vacuum.
The Behavior of Gases
Air exerts pressure on Earth because gravity
holds the particles in air within Earth’s
atmosphere.
The collisions of atoms and molecules in air
with objects results in atmospheric pressure.
A barometer is a device that is used to measure
atmospheric pressure.
The Behavior of Gases
The SI unit of pressure is the pascal (Pa).
Normal atmospheric pressure is about 100,000 Pa, that is, 100 kilopascals (kPa).
Two older units of pressure are commonly used.
millimeters of mercury (mm Hg)
atmospheres (atm)
Equivalents of different pressures are:
1 atm
101.3 kPa
760 mm Hg
The Behavior of Gases
Standard pressure is defined as 1 atm
Standard temperature is 0 °C
0 Kelvin is defined as absolute zero
The point at which all particle motion ceases
To convert from Celsius to Kelvin, use the following
relationship:
K = 273 + ° C
The Behavior of Gases
The gas laws are mathematical expressions
that describe the relationship between the
volume, pressure, temperature, and number
of particles of a gas
Boyle’s Law states that the volume of a fixed
mass of gas varies inversely with pressure at
constant temperature
P1 V1 = P2 V2
The Behavior of Gases
A balloon contains 30.0 L of helium gas at 103
kPa. What is the volume of the helium when
the balloon rises to an altitude where the
pressure is only 25.0 kPa? (Assume that the
temperature remains constant.)
The Behavior of Gases
Charles’s Law states that the volume of a fixed mass of gas at a constant pressure varies directly with the Kelvin temperature
V1 V2
T1 T2 =
The Behavior of Gases
A balloon inflated in a room at 24 °C has a
volume of 4.00 L. The balloon is then heated
to a temperature of 58 °C. What is the new
volume if the pressure remains constant?
The Behavior of Gases
Gay-Lussac’s Law states that
the pressure of a fixed mass
of gas at a constant volume
varies directly with the Kelvin
temperature
P1 P2
T1 T2 =
The Behavior of Gases
Aerosol cans carry labels warning not to
incinerate (burn) the cans or store them
above a certain temperature. The gas in a
used aerosol can is at a pressure of 103 kPa
at 25 °C. If the can is thrown onto a fire, what
will the pressure be when the temperature
reaches 928 °C?
The Behavior of Gases
The three gas laws can be combined to
create the Combined Gas Law
States the relationship between pressure, volume,
and temperature of a fixed amount of gas
V1P1 V2P2
T1 T2 =
The Behavior of Gases
The volume of a gas-filled balloon is 30.0 L at
313 K and 153 kPa pressure. What would
the volume be at standard temperature and
pressure (STP)?
The Behavior of Gases
Each of the gas laws describes how pressure,
temperature, and volume can change
None of those laws include how the number of
particles can change
The volume occupied by a gas at a specified
temperature and pressure depends on the number
of particles.
The number of moles of gas is directly proportional
to the number of particles.
The Behavior of Gases
The gas law that includes all four variables—
P, V, T, n—is called the ideal gas law.
PV = nRT
P = pressure
V =volume
n = mole (directly proportional to particles)
R = a constant
T = temperature
The Behavior of Gases
PV = nRT
We can solve for R, the ideal gas law constant,
because we know that 1 mole of gas occupies 22.4
L at STP (101.3 kPa and 273 K)
(101.3 kPa)(22.4 L) = R (1 mol)(273 K)
R = 8.31 L·kPa/ mol·K
The Behavior of Gases
At 34oC, the pressure inside a nitrogen-filled
tennis ball with a volume of 0.148 L is 212
kPa. How many moles of nitrogen gas are in
the tennis ball?
The Behavior of Gases
A deep underground cavern contains 2.24 x
106 L of methane gas (CH4) at a pressure of
1.50 atm and a temperature of 315 K. How
many grams of CH4 does the cavern
contain?
The Behavior of Gases
Real gases differ from ideal gases
An ideal gas is one that follows the gas laws at all
conditions of pressure and temperature.
Its particles could have no volume.
There could be no attraction between particles in the
gas.
Its collisions are elastic
The Behavior of Gases
Real gases differ from ideal gases
There is no gas for which these assumptions are
true.
So, an ideal gas does not exist, at many conditions of
temperature and pressure, a real gas behaves very
much like an ideal gas.
They differ most at low temperatures and high pressures
