chemistry - chp 13 - states of matter

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

Section 13.1Section 13.1The Nature of GasesThe Nature of Gases

OBJECTIVES:OBJECTIVES:DescribeDescribe the assumptions the assumptions of the “kinetic theory” as it of the “kinetic theory” as it applies to gases.applies to gases.


OBJECTIVES:OBJECTIVES:InterpretInterpret gas pressure in gas pressure in terms of kinetic theory.terms of kinetic theory.


OBJECTIVES:OBJECTIVES:DefineDefine the relationship the relationship between Kelvin temperature between Kelvin temperature and average kinetic energy.and average kinetic energy.


KineticKinetic refers to refers to motionmotion 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!

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#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 – defined as the force the force exerted by a gas per unit surface area exerted by a gas per unit surface area of an objectof an object Due to:Due to:a)a) force of collisionsforce of collisionsb)b) number of collisionsnumber of collisions No particles present? Then there cannot No particles present? Then there cannot

be any collisions, and thus no pressure – be any collisions, and thus no pressure – called a 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) Older units of pressure include Older units of pressure include

millimeters of mercury (mm Hg), and millimeters of mercury (mm Hg), and atmospheres (atm) – both of which atmospheres (atm) – both of which came from using a mercury barometercame from using a mercury barometer


Mercury BarometerMercury Barometer – Fig. 10.2, – Fig. 10.2, page 269 – a straight glass tube page 269 – a straight glass tube filled with Hg, and closed at one filled with Hg, and closed at one end; placed in a dish of Hg, with the end; placed in a dish of Hg, with the open end below the surfaceopen end below the surface At sea level, the mercury would rise to At sea level, the mercury would rise to

760 mm high at 25 760 mm high at 25 ooC- called one C- called one standard atmospherestandard atmosphere (atm) (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? heated? Particles absorb energy!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

OBJECTIVES:OBJECTIVES:IdentifyIdentify factors that factors that determine physical properties determine physical properties of a liquid.of a liquid.


OBJECTIVES:OBJECTIVES:DefineDefine “evaporation” in “evaporation” in terms of kinetic energy.terms of kinetic energy.


OBJECTIVES:OBJECTIVES:DescribeDescribe the equilibrium the equilibrium between a liquid and its between a liquid and its vapor.vapor.


OBJECTIVES:OBJECTIVES:IdentifyIdentify the conditions at the conditions at which boiling occurs.which boiling occurs.


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 FLOWGases and liquids can both FLOWHowever, 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 temperature decreasesdecreases 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 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

- Page 279

Questions:

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


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


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 10.2, p.277- Figure 10.2, p.277

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 the bp of a liquid at a pressure of at a pressure of 101.3 kPa (or standard pressure)101.3 kPa (or standard pressure)


Normal bp of water = Normal bp of water = 100 100 ooCC However, in Denver = However, in Denver = 95 95 ooCC, since , 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 aBoiling is a cooling processcooling 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


The The heat of vaporizationheat of vaporization of a liquid of a liquid is the energy that must be added in is the energy that must be added in order to maintain a constant temp order to maintain a constant temp while vaporization, or boiling occurs.while vaporization, or boiling occurs. For water at its normal boiling point of For water at its normal boiling point of

100 degrees Celcius, the heat of 100 degrees Celcius, the heat of vaporization is vaporization is 2259 Joules2259 Joules


The The heat of condensationheat of condensation is is thethe energy that must be removed in energy that must be removed in order to maintain constant temp order to maintain constant temp during condensationduring condensationCondensation is Condensation is exothermicexothermicFor water, the heat of For water, the heat of

condensation is is 2259 Joules condensation is is 2259 Joules per gram – the same as the heat per gram – the same as the heat of vaporizationof vaporization

Section 13.3Section 13.3The Nature of SolidsThe Nature of Solids

OBJECTIVES:OBJECTIVES:EvaluateEvaluate how the way how the way particles are organized particles are organized explains the properties of explains the properties of solids.solids.


OBJECTIVES:OBJECTIVES:IdentifyIdentify the factors that the factors that determine the shape of a determine the shape of a crystal.crystal.


OBJECTIVES:OBJECTIVES:ExplainExplain how allotropes of an how allotropes of an element are different.element are different.


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

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 (mp) is the 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, most ionic solids haveGenerally, 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


When a liquid is cooled, a temperature is When a liquid is cooled, a temperature is eventually reached at which the liquid begins to eventually reached at which the liquid begins to freeze. It changes into a solidfreeze. It changes into a solid

This temperature, which remains constant until This temperature, which remains constant until all the liquid has solidified at 1 atmosphere all the liquid has solidified at 1 atmosphere pressure, is called the pressure, is called the freezing point freezing point of the of the liquidliquid

While the liquid is cooling, the average kinetic While the liquid is cooling, the average kinetic energy of its particles decreases until it is low energy of its particles decreases until it is low enough for the attractive forces to be able to enough for the attractive forces to be able to hold the particles in the fixed positions hold the particles in the fixed positions characteristic of the solid phasecharacteristic of the solid phase

Heat of solidificationHeat of solidification The amount of heat needed to The amount of heat needed to

change change 1 gram of liquid water at 1 gram of liquid water at STP to 1 gram of ice at the same STP to 1 gram of ice at the same conditionsconditions

Heat of solidification = Heat of solidification = 334 Joules334 Joules

Heat of fusionHeat of fusion The amount of heat needed to The amount of heat needed to

change a unit mass of a change a unit mass of a substance from solid to liquid at substance from solid to liquid at STPSTP

Heat of fusion of ice = Heat of fusion of ice = 334 Joules334 Joules

Heating CurveHeating Curve

020406080

100120140160180200

0 1 2 3 4 5 6 7 8 9 10111213141516

A

B C

D E

F

Heat of Fusion Liquid

gas

Heat of vaporization

solidTe

mpe

ratu

re in

Cel

sius

Time in minutes

Cooling CurveCooling Curve

020406080100120140160180200

0 1 2 3 4 5 6 7 8 9 10111213141516

A

B C

D E

F

Tem

pera

ture

in C

elsi

us

Time in minutes

Heating CurveHeating Curve

020406080100120140160180200

0 1 2 3 4 5 6 7 8 910111213141516

Tem

pera

ture

in C

elsi

us

Time in minutes

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 dry ice (-78 Examples: iodine dry ice (-78

ooC); mothballs; solid air C); mothballs; solid air freshenersfresheners


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)


The diagram in your notes shows The diagram in your notes shows the phase diagram for waterthe phase 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

)

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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?

chemistry - chp 13 - states of matter

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