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CH110 CH110 Chapter 6: GasesChapter 6: Gases

Kinetic Molecular TheoryKinetic Molecular Theory

PressurePressure

Gas LawsGas Laws

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SolidSolid

LiquidLiquid

VaporVapor

Slow moving, Slow moving, dense,dense,Fixed shapeFixed shape

Moderate Moderate movement,movement,Dense,Dense,Takes shape of containerTakes shape of container

Fast moving, Fast moving, Low density,Low density,Expands to fill containerExpands to fill container

DensityDensity ShapeShape CompressibilityCompressibility

Small Small compressibility,compressibility,

Very smallVery small heat expansion heat expansion

Large Large compressibility,compressibility,Expands w/ heatExpands w/ heat

SmallSmallcompressibility,compressibility,

Small heat expansionSmall heat expansion

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1. All gases are made up of tiny particlestiny particles moving in moving in • straight linesstraight lines • in all directions • at various speeds.

Kinetic molecular theory of GasesKinetic molecular theory of Gases

Model to explain behavior of gases

VaporVapor

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3.3. V of a gas V of a gas = V of containerV of container

V of a gas is mostly empty space.

2. Particles far apart have no effect onno effect on each othereach other. (Don’t attract or repel)

Kinetic molecular theoryKinetic molecular theory

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Kinetic molecular theory Kinetic molecular theory

4. The ave KE ave KE as the TT

•The The average KE average KE is theis the same same for all for all gases atgases at thethe same T. same T.

TTKEKE

(K.E. (K.E. T) T)

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5. Gas molecules exert pressurepressure as they collide with container walls

The The > > thethe # # ofof collisionscollisions (per unit time), (per unit time), thethe > > thethe pressure pressure

Kinetic molecular theoryKinetic molecular theory

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6. E is conserved6. E is conservedwhen colliding with each other or container walls.

For an Ideal GasIdeal Gas CollisionsCollisions are perfectly elastic & no E is gained or lost. (Like billiard balls exchanging E.)

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Parameters forParameters forDescribing GasesDescribing Gases

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Parameter Symbol Description Units

PPressureForce per

unit area

mmHg (torr)

or atm

Volume V

No.of moles n No. of moles

of gasmole

Volume of

containerliter

Temperature TAbsolute temp

of gasK

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PressurePressure= = ForceForce per unit of per unit of Area.Area. Force

AreaAreaPP = = ForceForce

AreaArea

In the atmosphere, molecules of air (NN22, ,

OO22, Ar, H, Ar, H22OO, etc..) are constantly bouncing

off us.

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We live at the bottom of an ocean of air

Atmospheric PressureAtmospheric Pressure

Atmosphere:A sea of colorless, odorless gases surrounding the earth

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PressurePressureAt At higher elevationshigher elevations, there is , there is less less airair so the so the PP is less is less..

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Boiling Point Boiling Point = Temp where molecules = Temp where molecules

overcome atmospheric Pressureovercome atmospheric Pressure

Sea LevelSea Level

760 torr760 torrDenver (5280’)Denver (5280’)630 torr630 torr

Mt. Evans,CO(14,000’)Mt. Evans,CO(14,000’)

Mt. Everest(20,000’)Mt. Everest(20,000’)

467 torr467 torr

270 torr270 torr HH22OOHH22OO

= 100 oC

= 95 oC

= 87 oC

= 73 oC

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Measuring PressureMeasuring PressureAttempts to

pump water out of flooded

mines often failed because

HH22O can’t be O can’t be

lifted more than lifted more than 34 feet.34 feet.

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Measuring PressureMeasuring Pressure

TorricelliTorricelli believed the reason was that the P of atmosphere could not hold anything heavier than a 34’ column of water.

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Like drinking from a straw.

What causes the liquid to move up the straw to your mouth ?

Atmospheric Pressure Atmospheric Pressure

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34’ columnof water

1 Atm1 Atm

The atmosphere

would support a column of

H2O> 34 feet high.

Measuring PressureMeasuring Pressure

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Torricelli BarometerTorricelli BarometerPressure of the atmosphere supports aPressure of the atmosphere supports acolumn of column of Hg 760 mmHg 760 mm high. high.

1 atm

1 atm1 atm =760 mm Hg760 mm Hg760 torr760 torr29.92 in Hg14.7 lb/in2

101,325 Pa

vacuumvacuum

Mercury used because it’s so dense.

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Blood pressureBlood pressure (systolic over diastolic):most often in mm Hgmm Hg. (ex. 120/80)120/80)

MeteorologistsMeteorologists refer to pressure systems in mm or inches of Hg. ex. 30.01 in30.01 in

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STPSTPStandard Temperature & Standard Temperature & PressurePressure

1 atm

1 atm1 atm =760 mm Hg760 mm Hg760 torr760 torr29.92 in Hg14.7 lb/in2

101,325 Pa

00ooCC

273K273K

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Gas lawsGas lawsLaws that show relationships between volume and properties of gases

Boyle’s LawBoyle’s LawCharles’ LawCharles’ LawGay-Lussac’s LawGay-Lussac’s Law

Boyle’s LawBoyle’s LawCharles’ LawCharles’ LawGay-Lussac’s LawGay-Lussac’s Law

Avogadro’s LawAvogadro’s LawDalton’s LawDalton’s LawAvogadro’s LawAvogadro’s LawDalton’s LawDalton’s Law

CombinedCombinedGas LawGas Law

CombinedCombinedGas LawGas Law

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V V is is inversely proportionalinversely proportional to to PP

when T is constant.when T is constant.

If P goes downIf P goes downIf P goes downIf P goes down V goes upV goes upV goes upV goes up

PP

VV

PP VV

PP

VV

Boyle’s law: V vs PBoyle’s law: V vs P

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1 L1 L

Boyle’s law: V vs PBoyle’s law: V vs P2 L2 L

Drive to Drive to top of mountaintop of mountain - - ears start ears start poppingpopping. .

BreathingBreathing at high altitudes is at high altitudes is more more difficultdifficult because the pressure of O because the pressure of O22 is less.is less.

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It all “Boyle’s” down to Breathing in and out.

Boyle’s lawBoyle’s law

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Charles’s law: V vs TCharles’s law: V vs TThe The volume of a gasvolume of a gas is is directly proportionaldirectly proportional to the to the absolute temperatureabsolute temperature (K). (K).

T V

PP

If T goes upIf T goes upIf T goes upIf T goes up V goes upV goes upV goes upV goes up

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Gay-Lussac’s Law (PGay-Lussac’s Law (PT)T)

Pressure of a gas Pressure of a gas is is directly proportionaldirectly proportional to to

Absolute Temp (K) when Absolute Temp (K) when Volume is constant Volume is constant

PP11 = PP22

TT11 TT22

PP11 = PP22

TT11 TT22

P T

VV

If P goes upIf P goes upIf P goes upIf P goes up T goes upT goes upT goes upT goes up

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Boiling with and without a lid

At the boiling point, the pressureof the water vapor inside the bubbles equals the sum of the atmospheric pressure plus water pressure. As a result, the bubbles of water vapor are buoyed to the surface and escape.

The tight lid holds pressurizedvapor above the water surface,and this inhibits boiling. So,the boiling point is increased.Hotter water cooks more quickly.

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Avogadro’s lawAvogadro’s lawThe The volume of a gas volume of a gas is directly is directly

proportional to the proportional to the number of moleculesnumber of molecules

VV11 = VV22

nn11 nn22

VV11 = VV22

nn11 nn22

More moles of a gas, takes up more space.

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At Standard Temperature & Pressure At Standard Temperature & Pressure (STP)(STP)

V of 1 mole of gas = V of 1 mole of gas = 22.4 liters22.4 liters

Equal volumes of gas Equal volumes of gas (at same T and P)(at same T and P)

contain equal numbers of molecules.contain equal numbers of molecules.

Avogadro’s lawAvogadro’s law

At T = 273 KAt T = 273 K (0ºC) P = 1 atm1 atm (760 mm)

1 mol He1 mol He

4 g He4 g He

22.4 L22.4 L

1 mol He1 mol He

4 g He4 g He

22.4 L22.4 L

1 mol N1 mol N22

28 g N28 g N22

22.4 L22.4 L

1 mol N1 mol N22

28 g N28 g N22

22.4 L22.4 L

1 mol CO1 mol CO22

44 g CO44 g CO22

22.4 L22.4 L

1 mol CO1 mol CO22

44 g CO44 g CO22

22.4 L22.4 L

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Dalton’s law of Partial PressuresDalton’s law of Partial Pressures

The total pressure of a gas mix = sum of the partial pressures of each gas.

Pair = PN2 + PO2 + PCO2 + PH2O

PPTT == PP11 + P + P22 + P + P33 + ..... + .....

Each gas acts independently of the others.Each gas acts independently of the others.

Example: AirExample: Air

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Blood GasesBlood Gases

PPCOCO22 ~ 40 mm Hg ~ 40 mm Hg

Normal PO2 in the air =160 mm.

If drops

< 100 mm,

can’t diffuse into the blood.

Arterial Blood Gases (ABGs)Arterial Blood Gases (ABGs)

PPBGBG = = PPOO22 + + PPCOCO22

PPOO22 ~ 100 mm Hg ~ 100 mm Hg

PCO2 ~ 46 mm Hg

Venous Blood Gases (VBGs)Venous Blood Gases (VBGs)

PO2 ~ 40 mm Hg

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Temperature vs SolubilityTemperature vs SolubilityCold HCold H22O holds more gas than warm HO holds more gas than warm H22OO

If hot rivers lose too much dissolved OIf hot rivers lose too much dissolved O22

the fish can’t survive.the fish can’t survive.

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Carbonated beverages bottled cold.

Temperature vs SolubilityTemperature vs Solubility

Divers with bends often packed in ice for transport

to hyperbaric chamber.