Chapter 13 “States of Matter”. Section 13.1 The Nature of Gases Kinetic refers to motion Kinetic refers to motion The energy an object has because of

Chapter 13Chapter 13“States of Matter”“States of Matter”

Section 13.1Section 13.1The Nature of GasesThe Nature of Gases

KineticKinetic refers to motion refers to motion The energy an object has The energy an object has

because of it’s motion is called because of it’s motion is called kinetic energykinetic energy

The The kinetic theorykinetic theory states that the states that the tiny particles in tiny particles in all forms of matterall forms of matter are in are in constant motionconstant motion!!


Three basic assumptionsThree basic assumptions of the kinetic of the kinetic theory as it applies to gases:theory as it applies to gases:

#1#1. Gas is . Gas is composed of particlescomposed of particles-- usually molecules or atomsusually molecules or atoms Small, hard spheresSmall, hard spheres Insignificant volume; relatively far Insignificant volume; relatively far

apart from each otherapart from each other No attraction or repulsion between No attraction or repulsion between

particlesparticles


#2#2. Particles in a gas move rapidly . Particles in a gas move rapidly in in constant constant randomrandom motion motion Move in straight paths, changing Move in straight paths, changing

direction only when colliding with one direction only when colliding with one another or other objectsanother or other objects

Average speed of OAverage speed of O22 in air at 20 in air at 20 ooC is C is an amazing 1700 km/h!an amazing 1700 km/h!

Random walk is a very short distance Random walk is a very short distance


#3#3. Collisions are . Collisions are perfectly perfectly elasticelastic-- meaning kinetic energy meaning kinetic energy is transferred without loss from is transferred without loss from one particle to another- the total one particle to another- the total kinetic energy remains constantkinetic energy remains constant


Gas PressureGas Pressure – defined as the force – defined as the force exerted by a gas per unit surface exerted by a gas per unit surface area of an objectarea of an object Due to: a) Due to: a) force of collisionsforce of collisions, and b) , and b)

number of collisionsnumber of collisions No particles present? Then there No particles present? Then there

cannot be any collisions, and thus no cannot be any collisions, and thus no pressure – called a pressure – called a vacuumvacuum


Atmospheric pressureAtmospheric pressure results from results from the collisions of air molecules with the collisions of air molecules with objectsobjects Decreases as you climb a mountain Decreases as you climb a mountain

because the air layer thins out as because the air layer thins out as elevation increaseselevation increases

BarometerBarometer is the measuring device is the measuring device for atmospheric pressure, which is for atmospheric pressure, which is dependent upon weather & altitudedependent upon weather & altitude

Measuring PressureMeasuring PressureThe first device for measuring atmosphericpressure was developed by Evangelista Torricelli during the 17th century.

The device was called a “barometer”

Baro = weight Meter = measure Torricelli


The SI unit of pressure is the The SI unit of pressure is the pascal (Pa)pascal (Pa) At sea level, atmospheric pressure is At sea level, atmospheric pressure is

about 101.3 about 101.3 kilopascalskilopascals (kPa) (kPa) Other units of pressure include Other units of pressure include

millimeters of mercury (mm Hg), and millimeters of mercury (mm Hg), and atmospheres (atm) atmospheres (atm)

An Early An Early BarometerBarometer

The normal pressure due to the atmosphere at sea level can support a column of mercury that is 760 mm high.


Equal pressures:1 atm = 760 mm Hg = 101.3 kPaEqual pressures:1 atm = 760 mm Hg = 101.3 kPa Sample 13.1, page 387Sample 13.1, page 387 Most modern barometers do not Most modern barometers do not

contain mercury- too dangerouscontain mercury- too dangerous These are called These are called aneroid barometersaneroid barometers, ,

and contain a sensitive metal and contain a sensitive metal diaphragm that responds to the diaphragm that responds to the number of collisions of air moleculesnumber of collisions of air molecules

The Aneroid BarometerThe Aneroid Barometer


For gases, it is important to relate For gases, it is important to relate measured values to standardsmeasured values to standards Standard values are defined as a Standard values are defined as a

temperature of 0temperature of 0 o oC and a pressure of C and a pressure of 101.3 kPa, or 1 atm101.3 kPa, or 1 atm

This is called This is called Standard Standard Temperature and PressureTemperature and Pressure, or , or STPSTP


What happens when a substance is What happens when a substance is heated? Particles absorb energy!heated? Particles absorb energy! Some of the energy is storedSome of the energy is stored within within

the particles- this is potential energy, the particles- this is potential energy, and does not raise the temperatureand does not raise the temperature

Remaining energy speeds up the Remaining energy speeds up the particles (increases average kinetic particles (increases average kinetic energy)- thus energy)- thus increases temperatureincreases temperature


The particles in any collection have The particles in any collection have a wide range of kinetic energies, a wide range of kinetic energies, from very low to very high- but most from very low to very high- but most are somewhere in the middle, thus are somewhere in the middle, thus the term the term averageaverage kinetic energy kinetic energy is is usedused The higher the temperature, the wider The higher the temperature, the wider

the range of kinetic energiesthe range of kinetic energies


An increase in the average kinetic An increase in the average kinetic energy of particles causes the energy of particles causes the temperature to rise.temperature to rise. As it cools, the particles tend to move As it cools, the particles tend to move

more slowly, and the average K.E. more slowly, and the average K.E. declines.declines.

Is there a point where they slow down Is there a point where they slow down enough to enough to stopstop moving? moving?


The particles would have no kinetic The particles would have no kinetic energy at that point, because they energy at that point, because they would have no motionwould have no motion Absolute zeroAbsolute zero (0 K, or –273 (0 K, or –273 ooC) is C) is

the temperature at which the motion the temperature at which the motion of particles of particles theoretically ceasestheoretically ceases

This has never been reached, but This has never been reached, but about 0.5 x 10about 0.5 x 10-9-9 K has been achieved K has been achieved


The Kelvin temperature scale The Kelvin temperature scale reflects a reflects a direct relationshipdirect relationship between temperature and average between temperature and average kinetic energykinetic energyParticles of He gas at 200 K have Particles of He gas at 200 K have

twice the average kinetic energytwice the average kinetic energy as particles of He gas at 100 Kas particles of He gas at 100 K


Solids and liquids differ in their Solids and liquids differ in their response to temperatureresponse to temperature However, at any given temperature the However, at any given temperature the

particles of all substances, regardless of particles of all substances, regardless of their physical state, have the same their physical state, have the same average kinetic energyaverage kinetic energy

What happens to the temperature of a What happens to the temperature of a substance when the average kinetic substance when the average kinetic energy of its particles decreases?energy of its particles decreases?

Section 13.2Section 13.2The Nature of LiquidsThe Nature of Liquids

Liquid particlesLiquid particles are also in motion. are also in motion.Liquid particles are free to Liquid particles are free to slide slide

pastpast one another one anotherGases and liquids can both Gases and liquids can both

FLOW, as seen in Fig. 13.5, p.390FLOW, as seen in Fig. 13.5, p.390However, liquid particles However, liquid particles are are

attractedattracted to each other, whereas to each other, whereas gases are notgases are not


Particles of a liquid spin and vibrate Particles of a liquid spin and vibrate while they move, thus contributing while they move, thus contributing to their average kinetic energyto their average kinetic energy But, most of the particles But, most of the particles do notdo not have have

enough energy to escape into the enough energy to escape into the gaseous state; they would gaseous state; they would have to have to overcomeovercome their intermolecular their intermolecular attractions with other particlesattractions with other particles


The intermolecular attractions also The intermolecular attractions also reduce the amount of space between reduce the amount of space between particles of a liquidparticles of a liquidThus, liquids are more Thus, liquids are more densedense than than

gasesgases Increasing pressure on liquid has Increasing pressure on liquid has

hardly any effecthardly any effect on it’s on it’s volumevolume


Increasing the pressure also has Increasing the pressure also has little effect on the little effect on the volume of a volume of a solidsolid For that reason, liquids and solids are For that reason, liquids and solids are

known as the known as the condensed states of condensed states of mattermatter

Water in an open vessel or puddle Water in an open vessel or puddle eventually goes into the aireventually goes into the air


The conversion of a liquid to a gas The conversion of a liquid to a gas or vapor is called or vapor is called vaporizationvaporization When this occurs at the When this occurs at the surfacesurface of a of a

liquid that is liquid that is notnot boiling, the process boiling, the process is called is called evaporationevaporation

Some of the particles break away and Some of the particles break away and enter the gas or vapor state; but enter the gas or vapor state; but onlyonly those with the minimum kinetic energythose with the minimum kinetic energy


A liquid will also evaporate faster A liquid will also evaporate faster when heatedwhen heated Because the added heat increases Because the added heat increases

the average kinetic energy needed to the average kinetic energy needed to overcome the attractive forcesovercome the attractive forces

But, evaporation is a But, evaporation is a cooling processcooling process Cooling occurs because those with Cooling occurs because those with

the highest energy escape firstthe highest energy escape first


Particles left behind have Particles left behind have lowerlower average kinetic energies; thus the average kinetic energies; thus the temperature decreasestemperature decreases Similar to removing the fastest runner Similar to removing the fastest runner

from a race- the remaining runners from a race- the remaining runners have a lower average speedhave a lower average speed

Evaporation helps to keep our skin Evaporation helps to keep our skin cooler on a hot day, unless it is very cooler on a hot day, unless it is very humid on that day. Why?humid on that day. Why?


Evaporation of a liquid in a closed Evaporation of a liquid in a closed container is somewhat differentcontainer is somewhat different Fig. 13.6b on page 391 shows that no Fig. 13.6b on page 391 shows that no

particles can escape into the outside particles can escape into the outside airair

When some particles do vaporize, When some particles do vaporize, these collide with the walls of the these collide with the walls of the container producing container producing vapor pressurevapor pressure


Eventually, some of the particles will Eventually, some of the particles will return to the liquid, or return to the liquid, or condensecondense

After a while, the number of After a while, the number of particles evaporating will equal the particles evaporating will equal the number condensing- the space number condensing- the space above the liquid is now saturated above the liquid is now saturated with vaporwith vapor A dynamic equilibrium existsA dynamic equilibrium exists Rate of evaporationRate of evaporation = = rate of condensationrate of condensation


Note that there will Note that there will stillstill be particles be particles that evaporate and condensethat evaporate and condense But, there will be no But, there will be no NETNET change change

An An increase in temperatureincrease in temperature of a of a contained liquid increases the vapor contained liquid increases the vapor pressure- the particles have an pressure- the particles have an increased kinetic energy, thus more increased kinetic energy, thus more minimum energy to escapeminimum energy to escape


Note Table 13.1, page 392Note Table 13.1, page 392 The vapor pressure of a liquid can The vapor pressure of a liquid can

be determined by a device called a be determined by a device called a “manometer”“manometer”- Figure 13.7, p.393- Figure 13.7, p.393

The vapor pressure of the liquid will The vapor pressure of the liquid will push the mercury into the U-tubepush the mercury into the U-tube

A barometer is a type of manometerA barometer is a type of manometer


We now know the rate of We now know the rate of evaporation from an open container evaporation from an open container increases as heat is addedincreases as heat is added The heating allows larger numbers of The heating allows larger numbers of

particles at the liquid’s surface to particles at the liquid’s surface to overcome the attractive forcesovercome the attractive forces

Heating allows the average kinetic Heating allows the average kinetic energy of all particles to increaseenergy of all particles to increase


The The boiling pointboiling point (bp) is the (bp) is the temperature at which the temperature at which the vapor vapor pressure of the liquid is just equal to pressure of the liquid is just equal to the external pressure on the liquidthe external pressure on the liquidBubbles form Bubbles form throughoutthroughout the the

liquid, rise to the surface, and liquid, rise to the surface, and escape into the airescape into the air


Since the boiling point is where the Since the boiling point is where the vapor pressure equals external vapor pressure equals external pressure, the bp changes if the pressure, the bp changes if the external pressure changesexternal pressure changes

Normal boiling pointNormal boiling point-- defined as defined as the bp of a liquid at a pressure of the bp of a liquid at a pressure of 101.3 kPa (or standard pressure)101.3 kPa (or standard pressure)


Normal bp of water = 100 Normal bp of water = 100 ooCC However, in Denver = 95 However, in Denver = 95 ooC, since C, since

Denver is 1600 m above sea level and Denver is 1600 m above sea level and average atmospheric pressure is about average atmospheric pressure is about 85.3 kPa (Recipe adjustments?)85.3 kPa (Recipe adjustments?)

In In pressure cookerspressure cookers, which reduce , which reduce cooking time, water boils cooking time, water boils aboveabove 100 100 ooC C due to the increased pressuredue to the increased pressure

- Page 394

Not Boiling Normal Boiling Point @ 101.3 kPa = 100 oC

Boiling, but @ 34 kPa = 70 oC


AutoclavesAutoclaves, devices often used in the , devices often used in the past to sterilize medical instruments, past to sterilize medical instruments, operated much in a similar way – higher operated much in a similar way – higher pressure, thus higher boiling pointpressure, thus higher boiling point

Boiling is a cooling processBoiling is a cooling process much the much the same as evaporationsame as evaporationThose particles with highest KE Those particles with highest KE

escape firstescape first


Turning down the source of external Turning down the source of external heat drops the liquid’s temperature heat drops the liquid’s temperature below the boiling pointbelow the boiling point

Supplying more heat allows Supplying more heat allows particles to acquire enough KE to particles to acquire enough KE to escape- the escape- the temperature does not temperature does not go above the boiling pointgo above the boiling point, the liquid , the liquid only boils at a faster rateonly boils at a faster rate

- Page 394

Questions:

a. 60 oC b. about 20 kPa c. about 30 kPa

Section 13.3Section 13.3The Nature of SolidsThe Nature of Solids

Particles in a liquid are relatively Particles in a liquid are relatively free to movefree to moveSolid particles are Solid particles are notnot

Figure 13.10, page 396 shows Figure 13.10, page 396 shows solid particles tend to solid particles tend to vibratevibrate about fixed pointsabout fixed points, rather than , rather than sliding from place to placesliding from place to place


Most solids have particles packed Most solids have particles packed against one another in a highly against one another in a highly organized patternorganized pattern Tend to be dense and incompressibleTend to be dense and incompressible Do not flow, nor take the shape of Do not flow, nor take the shape of

their containertheir container Are still able to move, unless they Are still able to move, unless they

would reach absolute zerowould reach absolute zero


When a solid is heated, the particles When a solid is heated, the particles vibrate more rapidly as the kinetic vibrate more rapidly as the kinetic energy increasesenergy increases The organization of particles within The organization of particles within

the solid breaks down, and eventually the solid breaks down, and eventually the solid meltsthe solid melts

The The melting pointmelting point (mp) is the (mp) is the temperature a solid turns to liquidtemperature a solid turns to liquid


At the melting point, the disruptive At the melting point, the disruptive vibrations are strong enough to vibrations are strong enough to overcome the interactions holding overcome the interactions holding them in a fixed positionthem in a fixed position Melting point can be reversed by Melting point can be reversed by

cooling the liquid so it cooling the liquid so it freezesfreezes Solid liquidSolid liquid


Generally, Generally, most ionic solids have most ionic solids have high melting pointshigh melting points, due to the , due to the relatively strong forces holding them relatively strong forces holding them togethertogether Sodium chloride (an ionic compound) Sodium chloride (an ionic compound)

has a melting point = 801 has a melting point = 801 ooCC Molecular compounds have Molecular compounds have

relatively low melting pointsrelatively low melting points


Hydrogen chloride (a molecular Hydrogen chloride (a molecular compound) has a mp = -112 compound) has a mp = -112 ooCC

Not all solids melt- wood and cane Not all solids melt- wood and cane sugar tend to decompose when sugar tend to decompose when heatedheated

Most solid substances are Most solid substances are crystallinecrystalline in structure in structure


In a In a crystalcrystal, such as Fig. 13.10, , such as Fig. 13.10, page 396, the particles (atoms, page 396, the particles (atoms, ions, or molecules) are arranged in ions, or molecules) are arranged in a orderly, repeating, three-a orderly, repeating, three-dimensional pattern called a dimensional pattern called a crystal crystal latticelattice

All crystals have a regular shape, All crystals have a regular shape, which reflects their arrangementwhich reflects their arrangement


The The type of bondingtype of bonding that exists that exists between the atoms determines the between the atoms determines the melting points of crystalsmelting points of crystals

A crystal has sides, or A crystal has sides, or facesfaces The angles of the faces are a The angles of the faces are a

characteristic of that substance, and characteristic of that substance, and are always the same for a given are always the same for a given sample of that substancesample of that substance


Crystals are classified into Crystals are classified into seven seven groupsgroups, which are shown in Fig. , which are shown in Fig. 13.11, page 39713.11, page 397 The 7 crystal systems differ in terms The 7 crystal systems differ in terms

of the angles between the faces, and of the angles between the faces, and in the number of edges of equal in the number of edges of equal length on each facelength on each face


The shape of a crystal depends The shape of a crystal depends upon the arrangement of the upon the arrangement of the particles within itparticles within itThe smallest group of particles The smallest group of particles

within a crystal that retains the within a crystal that retains the geometric shape of the crystal is geometric shape of the crystal is known as a known as a unit cellunit cell


There are three kinds of unit There are three kinds of unit cells that can make up a cubic cells that can make up a cubic crystal system:crystal system:1. Simple cubic1. Simple cubic2. Body-centered cubic2. Body-centered cubic3. Face-centered cubic3. Face-centered cubic

90o angle

- Page 398


Some solid substances can exist in Some solid substances can exist in more than onemore than one form form Elemental carbon is an example, as Elemental carbon is an example, as

shown in Fig. 13.13, page 399shown in Fig. 13.13, page 399 1. 1. DiamondDiamond, formed by great pressure, formed by great pressure 2. 2. GraphiteGraphite, which is in your pencil, which is in your pencil 3. 3. BuckminsterfullereneBuckminsterfullerene (also called (also called

“buckyballs”) arranged in hollow “buckyballs”) arranged in hollow cages like a soccer ballcages like a soccer ball


These are called These are called allotropesallotropes of of carbon, because all are made of carbon, because all are made of pure carbon only , and all are solidpure carbon only , and all are solid

AllotropesAllotropes are two or more different are two or more different molecular forms of the same molecular forms of the same element in the same physical stateelement in the same physical state

Not all solids are crystalline, but Not all solids are crystalline, but instead are instead are amorphousamorphous


AmorphousAmorphous solids lack an ordered solids lack an ordered internal structureinternal structure Rubber, plastic, and asphalt are all Rubber, plastic, and asphalt are all

amorphous solids- their atoms are amorphous solids- their atoms are randomly arrangedrandomly arranged

Another example is glass- Another example is glass- substances cooled to a rigid state substances cooled to a rigid state without crystallizingwithout crystallizing


Glasses are sometimes called Glasses are sometimes called supercooled liquidssupercooled liquids The irregular internal structures of The irregular internal structures of

glasses are intermediate between glasses are intermediate between those of a crystalline solid and a free-those of a crystalline solid and a free-flowing liquidflowing liquid

Do not melt at a definite mp, but Do not melt at a definite mp, but gradually soften when heatedgradually soften when heated


When a crystalline solid is When a crystalline solid is shattered, the fragments tend to shattered, the fragments tend to have the same surface angles as have the same surface angles as the original solidthe original solid

By contrast, when amorphous solids By contrast, when amorphous solids such as glass is shattered, the such as glass is shattered, the fragments have irregular angles and fragments have irregular angles and jagged edgesjagged edges

Section 13.4Section 13.4Changes of StateChanges of State

OBJECTIVES:OBJECTIVES:IdentifyIdentify the conditions the conditions necessary for sublimation.necessary for sublimation.


OBJECTIVES:OBJECTIVES:DescribeDescribe how equilibrium how equilibrium conditions are represented conditions are represented in a phase diagram.in a phase diagram.


SublimationSublimation- the change of a - the change of a substance from a solid directly to substance from a solid directly to a vapor, without passing through a vapor, without passing through the liquid statethe liquid stateExamples: iodine (Fig. 13.14, p. Examples: iodine (Fig. 13.14, p.

401); dry ice (-78 401); dry ice (-78 ooC); mothballs; C); mothballs; solid air freshenerssolid air fresheners


Sublimation is useful in situations such Sublimation is useful in situations such as as freeze-dryingfreeze-drying foods- such as by foods- such as by freezing the freshly brewed coffee, and freezing the freshly brewed coffee, and then removing the water vapor by a then removing the water vapor by a vacuum pumpvacuum pump

Also useful in separating substances - Also useful in separating substances - organic chemists use it separate organic chemists use it separate mixtures and purify materialsmixtures and purify materials


The relationship among the solid, The relationship among the solid, liquid, and vapor states (or phases) liquid, and vapor states (or phases) of a substance in a sealed container of a substance in a sealed container are best represented in a single are best represented in a single graph called a graph called a phase diagramphase diagram

Phase diagramPhase diagram- gives the temperature - gives the temperature and pressure at which a substances and pressure at which a substances exists as solid, liquid, or gas (vapor)exists as solid, liquid, or gas (vapor)


Fig. 13.15, page 403 shows the Fig. 13.15, page 403 shows the phase diagram for waterphase diagram for water Each region represents a pure phaseEach region represents a pure phase Line between regions is where the Line between regions is where the

two phases exist in equilibriumtwo phases exist in equilibriumTriple pointTriple point is where all 3 curves is where all 3 curves

meet, the conditions where all 3 meet, the conditions where all 3 phases exist in equilibrium!phases exist in equilibrium!

Phase changes by Name

Critical Point

Temperature (oC)

Pres

sure

(kPa

)

- Page 403

Questions:


With a phase diagram, the With a phase diagram, the changes in mp and bp can be changes in mp and bp can be determined with changes in determined with changes in external pressureexternal pressure

What are the variables plotted What are the variables plotted on a phase diagram?on a phase diagram?

Documents

Chapter 13 “States of Matter”. Section 13.1 The Nature of Gases Kinetic refers to motion Kinetic refers to motion The energy an object has because of