Section 12.1 Gases
• Use the kinetic-molecular theory to explain the
behavior of gases.
• Describe how mass affects the rates of diffusion and
effusion.
• Explain how gas pressure is measured and calculate
the partial pressure of a gas.
kinetic energy: energy due to motion
Section 12.1 Gases (cont.)
kinetic-molecular theory
pressure
elastic collision
barometer
temperature
pascal
diffusion
atmosphere
Graham’s law of
effusion
Dalton’s law of partial
pressures
Gases expand, diffuse, exert pressure,
and can be compressed because they
are in a low density state consisting of
tiny, constantly-moving particles.
The Kinetic-Molecular Theory
• Kinetic-molecular theory explains the
different properties of solids, liquids, and
gases.
• The kinetic-molecular theory describes the
behavior of matter in terms of particles in
motion.
The Kinetic-Molecular Theory (cont.)
• Gases consist of small particles separated
by empty space.
• Gas particles are too far apart to experience
significant attractive or repulsive forces.
The Kinetic-Molecular Theory (cont.)
• Gas particles are in constant random
motion.
• An elastic collision is one in which no kinetic
energy is lost.
The Kinetic-Molecular Theory (cont.)
• Kinetic energy of a particle depends on
mass and velocity.
• Temperature is a measure of the average
kinetic energy of the particles in a sample of
matter.
Explaining the Behavior of Gases
• Great amounts of space exist between gas
particles.
• Compression reduces the empty spaces
between particles.
Explaining the Behavior of Gases (cont.)
• Gases easily flow past each other because
there are no significant forces of attraction.
• Diffusion is the movement of one material
through another.
• Effusion is a gas escaping through a tiny
opening.
Explaining the Behavior of Gases (cont.)
• Graham’s law of effusion states that the
rate of effusion for a gas is inversely
proportional to the square root of its molar
mass.
• Graham’s law also applies to diffusion.
Gas Pressure
• Pressure is defined as force per unit area.
• Gas particles exert pressure when they
collide with the walls of their container.
Gas Pressure (cont.)
• The particles in the earth’s atmosphere
exert pressure in all directions called air
pressure.
• There is less air pressure at high altitudes
because there are fewer particles present,
since the force of gravity is less.
Gas Pressure (cont.)
• Torricelli invented the barometer.
• Barometers are
instruments used
to measure
atmospheric air
pressure.
Gas Pressure (cont.)
• Manometers measure gas pressure in a
closed container.
Gas Pressure (cont.)
• The SI unit of force is the newton (N).
• One pascal(Pa) is equal to a force of one
Newton per square meter or N/m2.
• One atmosphere is equal to 760 mm Hg or
101.3 kilopascals.
Gas Pressure (cont.)
Gas Pressure (cont.)
• Dalton’s law of partial pressures states
that the total pressure of a mixture of gases
is equal to the sum of the pressures of all
the gases of the mixture.
• The partial pressure of a gas depends on the
number of moles, size of the container, and
temperature and is independent of the type
of gas.
Gas Pressure (cont.)
Ptotal = P1 + P2 + P3 +...Pn
• Partial pressure can be used to calculate the
amount of gas produced in a chemical
reaction.
Section 12.1 Assessment
The average of kinetic energy of particles
in a substance is measured by its ____.
A. mass
B. density
D
A
0%
C
D. pressure
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. temperature
Section 12.1 Assessment
One mole of oxygen in a 5.0 liter container
has the same partial pressure as one mol
of hydrogen in the same container. This is
a demonstration of what law?
A. law of conservation of mass
D
A
D. Dalton’s law of partial pressures 0%
C
C. law of conservation of energy
A. A
B. B
C. C
0%
0%
0%
D. D
B
B. law of definite proportions
Section 12.2 Forces of Attraction
• Describe intramolecular
forces.
• Compare and contrast
intermolecular forces.
polar covalent: a type
of bond that forms when
electrons are not shared
equally
dispersion force
dipole-dipole force
hydrogen bond
Intermolecular forces—including dispersion
forces, dipole-dipole forces, and hydrogen
bonds—determine a substance’s state at a given
temperature.
Intermolecular Forces
• Attractive forces between molecules cause
some materials to be solids, some to be
liquids, and some to be gases at the same
temperature.
Intermolecular Forces (cont.)
• Dispersion forces are weak forces that
result from temporary shifts in density of
electrons in electron clouds.
Intermolecular Forces (cont.)
• Dipole-dipole forces are attractions
between oppositely charged regions of
polar molecules.
Intermolecular Forces (cont.)
• Hydrogen bonds are special dipole-dipole
attractions that occur between molecules
that contain a hydrogen atom bonded to a
small, highly electronegative atom with at
least one lone pair of electrons, typically
fluorine, oxygen, or nitrogen.
Intermolecular Forces (cont.)
Section 12.2 Assessment
A hydrogen bond is a type of ____.
A. dispersion force
B. ionic bond
C. covalent bond
D
C
A
0%
B
D. dipole-dipole force
A. A
B. B
C. C
0%
0%
0%
D. D
Section 12.2 Assessment
Which of the following molecules can
form hydrogen bonds?
A. CO2
B. C2H6
D
A
0%
C
D. H2
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. NH3
Section 12.4 Phase Changes
• Explain how the addition
and removal of energy
can cause a phase
change.
• Interpret a phase
diagram.
phase change: a
change from one state
of matter to another
Section 12.4 Phase Changes
(cont.)
melting point
freezing point
vaporization
condensation
evaporation
deposition
vapor pressure
phase diagram
boiling point
triple point
Matter changes phase when energy is
added or removed.
Phase Changes That Require Energy
• Melting occurs when heat flows into a solid
object.
• Heat is the transfer of energy from an object
at a higher temperature to an object at a
lower temperature.
Phase Changes That Require Energy (cont.)
• When ice is heated, the ice eventually
absorbs enough energy to break the
hydrogen bonds that hold the water
molecules together.
• When the bonds break, the particles move
apart and ice melts into water.
• The melting point of a crystalline solid is the
temperature at which the forces holding the
crystal lattice together are broken and it
becomes a liquid.
Phase Changes That Require Energy (cont.)
• Particles with enough energy escape from
the liquid and enter the gas phase.
Phase Changes That Require Energy (cont.)
• Vaporization is the process by which a
liquid changes to a gas or vapor.
• Evaporation is vaporization only at the
surface of a liquid.
Phase Changes That Require Energy (cont.)
• In a closed container, the pressure exerted
by a vapor over a liquid is called vapor
pressure.
Phase Changes That Require Energy (cont.)
• The boiling point is the temperature at
which the vapor pressure of a liquid equals
the atmospheric pressure.
Phase Changes That Require Energy (cont.)
• Sublimation is the process by which a solid
changes into a gas without becoming a
liquid.
Phase Changes That Release Energy
• As heat flows from water to the
surroundings, the particles lose energy.
• The freezing point is the temperature at
which a liquid is converted into a crystalline
solid.
Phase Changes That Release Energy (cont.)
• As energy flows from water vapor, the
velocity decreases.
• The process by which a gas or vapor
becomes a liquid is called condensation.
• Deposition is the process by which a gas or
vapor changes directly to a solid, and is the
reverse of sublimation.
Phase Diagrams
• A phase diagram is a graph of pressure
versus temperature that shows in which
phase a substance will exist under different
conditions of temperature and pressure.
Phase Diagrams (cont.)
• The triple point is the point on a phase
diagram that represents the temperature
and pressure at which all three phases of a
substance can coexist.
Phase Diagrams (cont.)
• The phase diagram for different
substances are different from water.
Section 12.4 Assessment
The addition of energy to water molecules
will cause them to ____.
A. freeze
B. change to water vapor
D
A
0%
C
D. move closer together
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. form a crystal lattice
Section 12.4 Assessment
The transfer of energy from one object to
another at a lower temperature is ____.
A. heat
B. degrees
D
A
0%
C
D. electricity
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. conductivity
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Study Guide
Chapter Assessment
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Concepts in Motion
Section 12.1 Gases
Key Concepts
• The kinetic-molecular theory explains the properties
of gases in terms of the size, motion, and energy of
their particles.
• Dalton’s law of partial pressures is used to determine
the pressures of individual gases in gas mixtures.
• Graham’s law is used to compare the diffusion rates of
two gases.
Section 12.2 Forces of Attraction
Key Concepts
• Intramolecular forces are stronger than intermolecular
forces.
• Dispersion forces are intermolecular forces between
temporary dipoles.
• Dipole-dipole forces occur between polar molecules.
Section 12.3 Liquids and Solids
Key Concepts
• The kinetic-molecular theory explains the behavior of
solids and liquids.
• Intermolecular forces in liquids affect viscosity, surface
tension, cohesion, and adhesion.
• Crystalline solids can be classified by their shape and
composition.
Section 12.4 Phase Changes
Key Concepts
• States of a substance are referred to as phases
when they coexist as physically distinct parts of a
mixture.
• Energy changes occur during phase changes.
• Phase diagrams show how different temperatures and
pressures affect the phase of a substance.
760 mm Hg is equal to ____.
A. 1 Torr
B. 1 pascal
C. 1 kilopascal
D
C
A
0%
B
D. 1 atmosphere
A. A
B. B
C. C
0%
0%
0%
D. D
A collision in which no kinetic energy is
lost is a(n) ____ collision.
A. net-zero
B. elastic
D
A
0%
C
D. conserved
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. inelastic
Solids with no repeating pattern are ____.
A. ionic
B. crystalline
C. liquids
D
C
A
0%
B
D. amorphous
A. A
B. B
C. C
0%
0%
0%
D. D
What is the point at which all six phase
changes can occur?
A. the melting point
B. the boiling point
D
A
0%
C
D. the triple point
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. the critical point
What are the forces that determine a
substance’s physical properties?
A. intermolecular forces
B. intramolecular forces
D
A
0%
C
D. dispersal forces
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. internal forces
What do effusion rates depend on?
A. temperature of the gas
B. temperature and pressure
of the gas
D
A
0%
C
D. molar mass and temperature
of the gas
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. molar mass of the gas
A sealed flask contains helium, argon, and
nitrogen gas. If the total pressure is 7.5
atm, the partial pressure of helium is 2.4
atm and the partial pressure of nitrogen is
3.7 atm, what is the partial pressure of
argon?
A
D. 7.5 atm
D
0%
C. 1.4 atm
C
B. 6.1 atm
B
A. 1.3 atm
A. A
B. B
C. C
0%
0%
0%
D. D
Adding energy to a liquid will:
A. cause it to form crystal lattice
B. decrease the viscosity
D
A
0%
C
D. increase the velocity of the
particles
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. compress the particles
closer together
Hydrogen bonds are a special type of
____.
A. ionic bond
B. covalent bond
D
A
0%
C
D. dispersion force
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. dipole-dipole force
How many atoms of oxygen are present in
3.5 mol of water?
A. 2.1 x 1024
B. 3.5 x 1023
D
A
0%
C
D. 4.2 x 1024
A. A
B. B
C. C
0%
0%
0%
D. D
B
C. 6.02 x 1023
Click on an image to enlarge.
Table 12.4
Unit Cells
Table 12.5
Types of Crystalline Solids
Figure 12.30 Phase Diagrams
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