Transcript 13.4 Changes of State
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13.4 Changes of State >
Chapter 13 States of Matter 13.1 The Nature of Gases 13.2 The Nature of Liquids 13.3 The Nature of Solids
13.4 Changes of State
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13.4 Changes of State > CHEMISTRY & YOU
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Where does rainwater go when a puddle dries up?
Water cycles through much of the matter on Earth. Other elements, such as carbon and nitrogen, also cycle through Earth as solids, liquids, or gases.
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13.4 Changes of State >
Sublimation
Sublimation
When can sublimation occur?
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13.4 Changes of State >
Sublimation The change of a substance from a solid to a vapor without passing through the liquid state is called
sublimation
.
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13.4 Changes of State >
Sublimation The change of a substance from a solid to a vapor without passing through the liquid state is called
sublimation
.
• Sublimation can occur because solids, like liquids, have a vapor pressure.
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13.4 Changes of State >
Sublimation Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.
sublimation Solid Vapor deposition Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
13.4 Changes of State >
Sublimation Iodine is an example of a substance that undergoes sublimation.
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13.4 Changes of State >
Sublimation Iodine is an example of a substance that undergoes sublimation.
• The outer test tube contains solid iodine that is being gently heated.
• The inner test tube contains liquid water and ice.
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13.4 Changes of State >
Sublimation Iodine is an example of a substance that undergoes sublimation.
• The outer test tube contains solid iodine that is being gently heated.
• The inner test tube contains liquid water and ice.
• The iodine crystals at the bottom of the outer test tube change directly to iodine vapor.
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13.4 Changes of State >
Sublimation 10 Iodine is an example of a substance that undergoes sublimation.
• The outer test tube contains solid iodine that is being gently heated.
• The inner test tube contains liquid water and ice.
• The iodine crystals at the bottom of the outer test tube change directly to iodine vapor.
• When the vapor reaches the cool surface of the inner test tube, it goes directly from the gaseous to the solid state.
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13.4 Changes of State >
Sublimation Sublimation has many useful applications.
• Solid carbon dioxide (dry ice) is often used as a coolant for goods such as ice cream, which must remain frozen during shipment.
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13.4 Changes of State >
Sublimation 12 Sublimation has many useful applications.
• Solid carbon dioxide (dry ice) is often used as a coolant for goods such as ice cream, which must remain frozen during shipment.
– Because it sublimes, it does not produce a liquid as ordinary ice does when it melts.
– As it changes state, dry ice absorbs heat, keeping materials nearby cool and dry.
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13.4 Changes of State >
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Which of the following describes a solid undergoing sublimation?
A.
The vapor pressure exceeds the atmospheric pressure.
B.
The vapor pressure equals the atmospheric pressure.
C.
The vapor pressure is less than the atmospheric pressure.
D.
The vapor pressure is less than half the atmospheric pressure.
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13.4 Changes of State >
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Which of the following describes a solid undergoing sublimation?
A. The vapor pressure exceeds the atmospheric pressure.
B.
The vapor pressure equals the atmospheric pressure.
C.
The vapor pressure is less than the atmospheric pressure.
D.
The vapor pressure is less than half the atmospheric pressure.
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13.4 Changes of State >
Phase Diagrams
Phase Diagrams
How are the conditions at which phases are in equilibrium represented on a phase diagram?
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13.4 Changes of State >
Phase Diagrams The relationships among the solid, liquid, and vapor states (or phases) of a substance in a sealed container can be represented in a single graph.
• The graph is called a
phase diagram
.
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13.4 Changes of State >
Phase Diagrams 17 The relationships among the solid, liquid, and vapor states (or phases) of a substance in a sealed container can be represented in a single graph.
• The graph is called a
phase diagram
.
– A phase diagram gives the conditions of temperature and pressure at which a substance exists as a solid, liquid, or gas (vapor).
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13.4 Changes of State >
Phase Diagrams The conditions of pressure and temperature at which two phases exist in equilibrium are indicated on the phase diagram by a line separating the phases.
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13.4 Changes of State > Interpret
Graphs The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water.
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13.4 Changes of State > Interpret
Graphs The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water.
• In each of the curving regions of the phase diagram, water is in a single phase.
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13.4 Changes of State > Interpret
Graphs The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water.
• The curving line that separates water’s vapor phase from its liquid phase describes the equilibrium conditions for liquid and vapor.
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13.4 Changes of State > Interpret
Graphs 22 The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water.
• The other two lines describe the conditions for equilibrium between liquid water and ice and between water vapor and ice.
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13.4 Changes of State > Interpret
Graphs The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water.
• The point on the diagram at which all three lines meet is called the triple point.
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13.4 Changes of State >
Phase Diagrams The
triple point
describes the only set of conditions at which all three phases can exist in equilibrium with one another.
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13.4 Changes of State >
Phase Diagrams 25 The
triple point
describes the only set of conditions at which all three phases can exist in equilibrium with one another.
• For water, the triple point is a temperature of 0.016
° C and a pressure of 0.61 kPa.
• This flask is at the triple point. Freezing, melting, boiling, and condensation are all occurring at the same time in the flask.
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13.4 Changes of State > CHEMISTRY & YOU Describe how water might move from Earth’s surface to Earth’s atmosphere and back again as part of the water cycle. Be sure to include any phase changes that occur in your description.
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13.4 Changes of State > CHEMISTRY & YOU Describe how water might move from Earth’s surface to Earth’s atmosphere and back again as part of the water cycle. Be sure to include any phase changes that occur in your description.
Liquid water evaporates from Earth’s surface and rises to the atmosphere. There, it forms clouds and condenses as rain that falls back to Earth’s surface.
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13.4 Changes of State >
Phase Diagrams By referring to the phase diagram of water, you can determine what happens if you melt ice or boil water at pressures less than 101.3 kPa.
• A decrease in pressure lowers the boiling point and raises the melting point.
• An increase in pressure will raise the boiling point and lower the melting point.
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Phase Diagrams 29 Below the triple point, the vapor and liquid cannot exist in equilibrium.
• Increasing the pressure won’t change the vapor to a liquid.
• The solid and vapor are in equilibrium at temperatures below 0.016
° C.
• With an increase in pressure, the vapor begins to behave more like a solid.
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13.4 Changes of State >
Phase Diagrams For years, the accepted hypothesis for how ice-skaters move along the ice was the following.
• The blades of the skates exert pressure, which lowers the melting point of the ice.
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Phase Diagrams 31 For years, the accepted hypothesis for how ice-skaters move along the ice was the following.
• The blades of the skates exert pressure, which lowers the melting point of the ice.
• The ice melts, and a film of water forms under the blades of the skates.
• This film acts as a lubricant, enabling the skaters to glide gracefully over the ice.
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13.4 Changes of State >
Phase Diagrams This hypothesis fails to explain why skiers glide nicely on another solid form of water — snow.
• Wide skis exert much less pressure per unit area of snow than narrow skate blades exert on ice.
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13.4 Changes of State >
Phase Diagrams 33 This hypothesis fails to explain why skiers glide nicely on another solid form of water — snow.
• Wide skis exert much less pressure per unit area of snow than narrow skate blades exert on ice.
• Recent research shows that the surface of ice has a slippery, water like surface layer that exists well below ice’s melting point.
• The liquid-like surface layer provides lubrication needed for smooth skating and skiing.
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13.4 Changes of State >
Describe the meaning of a line in a phase diagram.
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13.4 Changes of State >
Describe the meaning of a line in a phase diagram.
Along a line in a phase diagram, two phases are in equilibrium with each other.
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13.4 Changes of State >
Key Concepts 36
Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.
The conditions of pressure and temperature at which two phases exist in equilibrium are indicated on a phase diagram by a line separating the two regions representing the phases.
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13.4 Changes of State >
Glossary Terms 37 •
sublimation:
the process in which a solid changes to a gas or vapor without passing through the liquid state •
phase diagram:
a graph showing the conditions at which a substance exists as a solid, liquid, or vapor •
triple point:
the point on a phase diagram that represents the only set of conditions at which all three phases exist in equilibrium with one another Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.
13.4 Changes of State > BIG
IDEA
Kinetic Theory
• The state of a substance is determined by conditions of pressure and temperature.
• Low pressures and high temperatures favor gases, in which particles move randomly in constant, high-speed motion.
• At higher pressures and lower temperatures, the particles slow down and exert attractive forces on one another, producing a liquid.
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13.4 Changes of State > BIG
IDEA 39
Kinetic Theory
• At still higher pressures and lower temperatures, the particles become fixed in orderly arrangements, producing solids.
• A substance changes state when there is a change in the balance between the random motion of its particles and the attractions among those particles.
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13.4 Changes of State > END OF 13.4
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