 Gases
are fluids
◦ Fluids are any substance that flows
 Gases
are highly compressible
◦ Example: Tire pressure
 Gases
completely fill containers
 Gases have lower densities than
liquids and solids
 KMT
describes the motion
of the particles
◦Particles have the same
motion as billiard balls
http://intro.chem.okstate.edu/NSFCCLI
/GasLaw/GLP.htm
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Assumptions:
Gas molecules are in constant, random motion
Gas molecules are separated by large distances
Gas molecules have no attractive/repulsive forces
Collisions are considered to be perfectly elastic ( no
energy is lost )

Temperature and energy of gases are directly
proportional
◦ As the temperature increases, kinetic energy of the
molecules increases
◦ As temperature decreases, kinetic energy will also
decrease
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At sea level, the standard gas pressure is 1
atmosphere
Pressure is the force exerted by gas
molecules
Standard Temperature and Pressure (STP) is
equal to 1 atm and 0 °C.
Note:1 ATM is measured from the surface of
the ocean (sea level) to the top of the sky
(stratosphere)
Atmosphere ( atm)
Torr / millimeter of mercury mm Hg
Pounds per square inch (psi)
Pascal of kilo Pascal (Pa or kPa)
Conversions vs. 1 ATM
760 mm Hg or Torr
14.7 psi
101.325 kPa
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
Convert 72.7 atmospheres (atm) into
kilopascals (kPa)
Convert 31.2 psi to ATM
 Variables
in Gas Equations:
◦P = Pressure (kPa or atm)
◦V = Volume (L)
◦T = Temperature (K)
◦n = amount of gas (moles)

States that for a fixed amount of gas at
constant temperature the volume of the gas
is inversely proportional to the pressure of a
gas
Pressure
Volume
P1V1  P2V2
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Example Problem
◦ The pressure on 2.50 L of anesthetic gas changes
from 105 kPa to 40.5 kPa. What will be the new
volume if the temperature remains constant?
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Example Problem
◦ A high-altitude balloon contains 30.0 L of helium
gas at 103 kPa. As the balloon rises, you record a
new volume of 35.0 L. What is the atmospheric
pressure in kPa? (Assume constant temperature)

States that the volume of a gas is directly
proportional to the Kelvin temperature if the
pressure remains constant
Temperature
V1 V2

T1 T2
Volume

Example Problem
◦ The air in a hot air balloon has a volume of 400.0 L
at 30.0°C (303 K). What will the volume be if the
temperature is raised to 120.0 °C (393 K)?

Example Problem
◦ An aerosol can has a volume of 3.00 x 102 mL at
150.0°C is heated until its volume is 6.00 x 102 mL.
What is the new temperature (in K) of the gas if
pressure remains constant?

States that the pressure of a gas is directly
proportional to the Kelvin temperature if the
volume remains constant
Temperature
Pressure
P1 P2

T1 T2

Example Problem
◦ The gas left in a used aerosol can is at a pressure of
103 kPa at 25 °C. If this can is thrown onto a fire,
what is the pressure of the gas when its
temperature reaches 928 °C?

Example Problem
◦ A sealed cylinder of gas contains nitrogen gas at
1.00 x 103 kPa pressure and a temperature of 20.0
°C. The cylinder is left in the sun, and the
temperature of the gas increases to 50.0 °C. What is
the new pressure in the cylinder?

A single equation that combines all the gas
laws:

Example Problem
◦ A gas takes up a volume of 17 liters, has a pressure
of 2.3 atm, and a temperature of 299 K. If I raise
the temperature to 350 K and lower the pressure to
1.5 atm, what is the new volume of the gas?
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Relates the gas laws and the amount of gas
Requires the gas constant, R
◦ R can be a different number depending on the units
kPa L
R  8.31
mol K
atm L
R  0.08205
mol K
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Example Problem
◦ A container of 3.0 L of nitrogen (N2) is at a pressure
of 4.5 x 102 kPa and a temperature of 39 °C. How
many grams of N2 are in the container?

Example Problem
◦ What pressure will be exerted by 0.450 mol of a gas
at 25.0 °C if it is contained in a 0.650 L vessel?
 Equal
volumes of gases at the
same temperature and pressure
contain equal numbers of
particles
 Due mainly to the large amount of
empty space between particles
◦ From this, scientists have determined
that 1 mol = 22.4 L at STP

Why?
◦ Tennis balls vs. Bowling balls