# 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.

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Section 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

Section 12.1 Gases (cont.) kinetic-molecular theory elastic collision
temperature diffusion Graham’s law of effusion pressure barometer pascal atmosphere 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. Section 12-1

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. Section 12-1

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. Section 12-1

The Kinetic-Molecular Theory (cont.)
Gas particles are in constant random motion. An elastic collision is one in which no kinetic energy is lost. Section 12-1

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. Section 12-1

Explaining the Behavior of Gases
Great amounts of space exist between gas particles. Compression reduces the empty spaces between particles. Section 12-1

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. Section 12-1

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. Section 12-1

Pressure is defined as force per unit area.
Gas Pressure Pressure is defined as force per unit area. Gas particles exert pressure when they collide with the walls of their container. Section 12-1

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. Section 12-1

Torricelli invented the barometer.
Gas Pressure (cont.) Torricelli invented the barometer. Barometers are instruments used to measure atmospheric air pressure. Section 12-1

Manometers measure gas pressure in a closed container.
Gas Pressure (cont.) Manometers measure gas pressure in a closed container. Section 12-1

The SI unit of force is the newton (N).
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 kilopascals. Section 12-1

Gas Pressure (cont.) Section 12-1

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. Section 12-1

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

A B C D Section 12.1 Assessment
The average of kinetic energy of particles in a substance is measured by its ____. A. mass B. density C. temperature D. pressure A B C D Section 12-1

A B C D 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 B. law of definite proportions C. law of conservation of energy D. Dalton’s law of partial pressures A B C D Section 12-1

Section 12.2 Forces of Attraction
Describe intramolecular forces. polar covalent: a type of bond that forms when electrons are not shared equally Compare and contrast intermolecular forces. 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. Section 12-2

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. Section 12-2

Intermolecular Forces (cont.)
Dispersion forces are weak forces that result from temporary shifts in density of electrons in electron clouds. Section 12-2

Intermolecular Forces (cont.)
Dipole-dipole forces are attractions between oppositely charged regions of polar molecules. Section 12-2

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. Section 12-2

Intermolecular Forces (cont.)
Section 12-2

A B C D Section 12.2 Assessment A hydrogen bond is a type of ____.
A. dispersion force B. ionic bond C. covalent bond D. dipole-dipole force A B C D Section 12-2

A B C D Section 12.2 Assessment
Which of the following molecules can form hydrogen bonds? A. CO2 B. C2H6 C. NH3 D. H2 A B C D Section 12-2

Section Phase Changes Explain how the addition and removal of energy can cause a phase change. phase change: a change from one state of matter to another Interpret a phase diagram. Section 12-4

Section 12.4 Phase Changes (cont.)
melting point vaporization evaporation vapor pressure boiling point freezing point condensation deposition phase diagram triple point Matter changes phase when energy is added or removed. Section 12-4

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. Section 12-4

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. Section 12-4

Phase Changes That Require Energy (cont.)
Particles with enough energy escape from the liquid and enter the gas phase. Section 12-4

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. Section 12-4

Phase Changes That Require Energy (cont.)
In a closed container, the pressure exerted by a vapor over a liquid is called vapor pressure. Section 12-4

Phase Changes That Require Energy (cont.)
The boiling point is the temperature at which the vapor pressure of a liquid equals the atmospheric pressure. Section 12-4

Phase Changes That Require Energy (cont.)
Sublimation is the process by which a solid changes into a gas without becoming a liquid. Section 12-4

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. Section 12-4

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. Section 12-4

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. Section 12-4

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. Section 12-4

The phase diagram for different substances are different from water.
Phase Diagrams (cont.) The phase diagram for different substances are different from water. Section 12-4

A B C D Section 12.4 Assessment
The addition of energy to water molecules will cause them to ____. A. freeze B. change to water vapor C. form a crystal lattice D. move closer together A B C D Section 12-4

A B C D Section 12.4 Assessment
The transfer of energy from one object to another at a lower temperature is ____. A. heat B. degrees C. conductivity D. electricity A B C D Section 12-4

End of Section 12-4

Standardized Test Practice Image Bank Concepts in Motion
Chemistry Online Study Guide Chapter Assessment Standardized Test Practice Image Bank Concepts in Motion Resources Menu

Graham’s law is used to compare the diffusion rates of two gases.
Section 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. Study Guide 1

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. Study Guide 2

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. Study Guide 3

Energy changes occur during phase changes.
Section 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. Study Guide 4

A B C D 760 mm Hg is equal to ____. A. 1 Torr B. 1 pascal
C. 1 kilopascal D. 1 atmosphere A B C D Chapter Assessment 1

A collision in which no kinetic energy is lost is a(n) ____ collision.
A. net-zero B. elastic C. inelastic D. conserved A B C D Chapter Assessment 2

A B C D Solids with no repeating pattern are ____. A. ionic
B. crystalline C. liquids D. amorphous A B C D Chapter Assessment 3

A B C D What is the point at which all six phase changes can occur?
A. the melting point B. the boiling point C. the critical point D. the triple point A B C D Chapter Assessment 4

What are the forces that determine a substance’s physical properties?
A. intermolecular forces B. intramolecular forces C. internal forces D. dispersal forces A B C D Chapter Assessment 5

A B C D What do effusion rates depend on? A. temperature of the gas
B. temperature and pressure of the gas C. molar mass of the gas D. molar mass and temperature of the gas A B C D STP 1

A sealed flask contains helium, argon, and nitrogen 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. 1.3 atm B. 6.1 atm C. 1.4 atm D. 7.5 atm A B C D STP 2

A B C D Adding energy to a liquid will:
A. cause it to form crystal lattice B. decrease the viscosity C. compress the particles closer together D. increase the velocity of the particles A B C D STP 3

A B C D Hydrogen bonds are a special type of ____. A. ionic bond
B. covalent bond C. dipole-dipole force D. dispersion force A B C D STP 4

A B C D How many atoms of oxygen are present in 3.5 mol of water?
A. 2.1 x 1024 B. 3.5 x 1023 C x 1023 D. 4.2 x 1024 A B C D STP 5

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Table 12.5 Types of Crystalline Solids Figure 12.30 Phase Diagrams
Table 12.4 Unit Cells Table 12.5 Types of Crystalline Solids Figure Phase Diagrams CIM

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