Gases
Packet 6 of 9
Chapter 14
1
Vocabulary
• Kinetic Molecular
theory
• Brownian motion
• Pressure
• Pascal (Pa)
• Barometer
• Diffusion
• Boltzmann’s constant
•
•
•
•
•
Molar volume
Ideal gas
Charles’ Law
Boyle’s Law
Atmospheric Pressure
(p. 445)
2
Overview Page
• This page in your packet is designed to be
a summary with formulas and sample
problems of the work you will learn in this
packet.
• Make sure you complete this page before
you take the test.
3
Graphing Exercises
• These activities are designed to help you
see the shapes of the gas laws we are
studying.
• Read the directions carefully
• Work in PENCIL!
Activity 2-4 and 2-6 in your
packet
4
Kinetic Molecular Theory (KMT)
• The theory that explains the observed
thermal and physical properties of matter
in terms of the average behavior of a
collection of atoms and molecules
• 3 parts– 1. All matter is made up of tiny particles.
2. These particles are in constant motion.
3. Collisions between these particles are
perfectly elastic.
5
KMT of gases
• Postulates
• A gas consists of a collection of small particles traveling
in straight-line motion and obeying Newton's Laws.
• The molecules in a gas occupy no volume (that is, they
are points). (we know that is not correct, but it helps our
model)
• Collisions between molecules are perfectly elastic (that is,
no energy is gained or lost during the collision).
• There are no attractive or repulsive forces between the
molecules. (we know that is not correct, but it helps our
model)
• The average kinetic energy of a molecule is 3kT/2. (T is
the absolute temperature and k is the Boltzmann constant
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Properties of Gases
• Molecules move quickly
• No definite shape
• No definite volume
• Molecules have low attractive forces to
each other
• They are translucent or transparent
• These basics determine the following
properties
and
behaviors
of
gases
Slides 5—8 are on your test. You might want to take some notes!
7
Properties of Gases
• Pressure: The force that gas molecules exert on
the side of the container
• Diffusion- The ability of a gas to move
through air
• Compressibility-Gas molecules can be
pushed together thereby decreasing the volume
Slides 5—8 are on your test. You might want to take some notes!
8
Properties of Gases
• Low Density -Gas molecules tend to
spread out having few molecules per
volume. This makes the density low
• Expansion-Gases expand to the volume of
their container
• Temperature and Pressure -Gases will
have different volumes at different
pressures and temperatures.
Slides 5—8 are on your test. You might want to take some notes!
9
STP
• Standard Temperature and Pressure
• Abbreviated STP
• The temperature and pressure scientists
use to study gases
• Standard temperature: 273 Kelvin or 0°C
• Standard pressure: 1 atm, 760 torrs, 760
mmHg or 101.3 kPa
Slides 5—8 are on your test. You might want to take some notes!
10
Review-Temperature Formulas
• Conversion Formulas
• You must be able to
convert between temp.
units!
• Make sure you can
convert Celsius to
Kelvins easily.
5
C  F - 32 
9
K  C  273
C  K - 273
9
F  C  32
5
11
Pressure Conversion Factorsreview
• 760 mmHg = 101.3 kPa = 1 atm = 760 torrs
• Convert the following using factor
labeling:
4.5 atm = ____torrs
365 kPa =____atm
Worksheet: Practice
Pressure Conversions
12
Example of an Early Barometer
The normal pressure due to
the atmosphere at sea level
can support a column of
mercury that is 760 mm high.
Variations in atmospheric
pressure affects the weather!
13
Manometers
• A device that
measures the
pressure of a
contained gas.
14
Avogadro’s Law
• The volume-amount fraction will always be the
same value if the pressure and temperature
remain constant.
• Relates Volume and moles
• A direct relationship
V1 V2

n1 n 2
V= volume
n = number of moles
15
Dalton’s Law
• Dalton's Law of Partial Pressures: each gas in a
mixture creates pressure as if the other gases
were not present. The total pressure is the sum
of the pressures created by the gases in the
mixture.
• Ptotal = P1 + P2 + P3 + .... + Pn
– Where n is the total number of gases in the mixture.
• The only necessity is that the two gases do not
interact in some chemical fashion, such as
reacting with each other.
• The pressure each gas exerts in mixture is called
its partial pressure.
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Boyle’s Law
• Always involve constant
temperature!
• When the temperature
and of a gas is held
constant its volume is
inversely proportional to
its pressure. (As one
increases the other one
decreases)
• Inverse = indirect
V2 P1

V1 P2
Animation of Boyle’s
Law
17
Boyle’s Law Sample:
• If a sample of gas has a volume of
100 cm3 when the pressure is 150 kPa.
What is the its volume in cm3 when the
pressure is increased to 200 kPa?
• Read Applications of Boyle’s Law on
page 452
Worksheet: Gas Law
Problems-Boyle’s Law
Lab: Gas Laws
Exploration (online)
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Charles’ Law
• If the pressure is
constant, the
volume of a fixed
mass of a gas is
directly
proportional to its
Kelvin
temperature.
•
V2 T2

V1 T1
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Sample Charles’ Law Problem
• A balloon inflated in an air conditioned
room at 27.0°C has a volume of 4.00 L. If
It is heated to 57.0 °C and the pressure
remains constant what is the new
volume?
Worksheet: Gas Law
Problems- Charles’ Law
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Gay-Lussac’s Law
• The pressure of a
gas is directly
proportional to the
Kelvin temperature
if the volume
remains constant.
P2 T2

P1 T1
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Sample Gay-Lussac’s Problem
• Example: A gas in an aerosol can is at a
pressure of 1.00 atm and 27.0 °C. If the
can is thrown into a fire what is the
internal pressure of the gas if the
temperature reaches 927°C?
Worksheet: Gas Law
Problems- Gay-Lusac’s Law
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Combined Gas Law
• Combines all the gas laws into onetemperature must be in Kelvin
V2 P1 T2
 
V1 P2 T1
Worksheet: Combined Gas Law
Problems
23
Ideal Gas Law
• Allows us to calculate about gases under
any set of conditions.
–
–
–
–
Moles
Volume
Temperature
Pressure
24
Ideal Gas Law
Gas law constant!
PV  nRT
Pressure in ATM
Volume in
LITERS
Number of
moles
Temperature in
Kelvin
25
Working Ideal
Gas Law Problems
• Be very careful that you use the correct
units!
–
–
–
–
Atm
Liters
Moles
Kelvins
• Anything else must be converted BEFORE
substituting into the equation!
Worksheet: Ideal Gas
Law
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Stoichiometry with Gases
• Under the conditions of STP
– 1 mole =22.4 L of any gas
– Normal Volume to Volume problem
• If the conditions are NOT at STP
– Use the Ideal Gas Law (PV =nRT)
– Find n (number of moles)
– Continue to solve your problem
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