13.4 Changes of State > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 13 States of Matter 13.1 The Nature of Gases

Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved.

13.4 Changes of State >13.4 Changes of State >

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Chapter 13States of Matter

13.1 The Nature of Gases13.2 The Nature of Liquids13.3 The Nature of Solids

13.4 Changes of State



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Where does rainwater go when a puddle dries up?

CHEMISTRY & YOUCHEMISTRY & YOU

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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SublimationSublimation

Sublimation

When can sublimation occur?



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The change of a substance from a solid to a vapor without passing through the liquid state is called sublimation.



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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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Sublimation occurs in solids with vapor pressures that exceed atmospheric pressure at or near room temperature.

Solid Vaporsublimation

deposition



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Iodine is an example of a substance that undergoes sublimation.



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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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• The iodine crystals at the bottom of the outer test tube change directly to iodine vapor.



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• 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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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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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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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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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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Phase DiagramsPhase Diagrams

Phase Diagrams

How are the conditions at which phases are in equilibrium represented on a phase diagram?



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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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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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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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The phase diagram of water shows the relationship among pressure, temperature, and the physical states of water.

Interpret GraphsInterpret Graphs



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• In each of the curving regions of the phase diagram, water is in a single phase.



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• 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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• The other two lines describe the conditions for equilibrium between liquid water and ice and between water vapor and ice.



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• The point on the diagram at which all three lines meet is called the triple point.



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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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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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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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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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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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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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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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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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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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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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Describe the meaning of a line in a phase diagram.



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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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Key ConceptsKey Concepts

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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Glossary TermsGlossary Terms

• 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



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Kinetic Theory

BIG IDEABIG IDEA

• 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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Kinetic Theory

BIG IDEABIG IDEA

• 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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END OF 13.4END OF 13.4

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13.4 Changes of State > 1 Copyright © Pearson Education, Inc., or its affiliates. All Rights Reserved. Chapter 13 States of Matter 13.1 The Nature of Gases