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Bires, 2007

Chapter 10 & 11: Chapter 10 & 11:

GasesGases

Chapter 10:

Page 300-330

Chapter 11:

Page 332-359

Chlorine gas was used as a weapon in WWI

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Bires, 2007 Slide 2

Kinetic Molecular TheoryKinetic Molecular Theory all matter is all matter is made up of particlesmade up of particles (atoms) in (atoms) in

random and random and constant motionconstant motion. (colliding). (colliding) Gases have very low densityGases have very low density

particles are spaced far apart.particles are spaced far apart. Gases are compressible.Gases are compressible.

Extreme pressures-gases will compress until they Extreme pressures-gases will compress until they become liquids become liquids (or solids, CO(or solids, CO22))..

Adding heatAdding heat to a system to a system increases the increases the temperaturetemperature … … Temperature = Temperature = measure of the measure of the average kinetic average kinetic

energy of the particlesenergy of the particles.. Increasing the Increasing the pressurepressure of a gas, of a gas,

increases the increases the densitydensity of the gas of the gas - the number of - the number of particles in a given space.particles in a given space.

Kinetic Energy of Gases.mov

221 mvKE

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Bires, 2007 Slide 3

IdealIdeal and and RealReal Gases Gases Ideal Gas:Ideal Gas:

Imaginary, perfect gas – makes calculations Imaginary, perfect gas – makes calculations easiereasier

Real Gas:Real Gas: Gas that actually behaves in reality…Gas that actually behaves in reality… When compressed, When compressed, real gases will form liquidsreal gases will form liquids, ,

and even exhibit liquid-like behaviors when and even exhibit liquid-like behaviors when still in gas form.still in gas form.

Real gas molecules interact with each other -Real gas molecules interact with each other -causing them to travel in causing them to travel in non-linear pathsnon-linear paths and and collide “collide “inelasticallyinelastically.”.”

With real gases, the With real gases, the sizesize of the gas molecules of the gas molecules effects their behavioreffects their behavior..

Ideal gasses

Real Gasses

RealGases.swf

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Bires, 2007 Slide 4

Gases in our atmosphereGases in our atmosphere

NitrogenNitrogen--7878%% OxygenOxygen--2121%% ArgonArgon-<-<11%% TraceTrace amounts of CO amounts of CO22, Ne, He, CH, Ne, He, CH44, Kr, H, Kr, H22, ,

OO33, and others, and others.. Some gases function as Some gases function as greenhouse greenhouse

gasesgases, and work to , and work to hold heat on the hold heat on the earth’s surfaceearth’s surface..

Some gases function to Some gases function to block harmful UV block harmful UV radiationradiation energy from the sun. energy from the sun.

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Bires, 2007 Slide 5

The Greenhouse The Greenhouse EffectEffect

The sun’s energy travels through space and The sun’s energy travels through space and warms the surface of the earth.warms the surface of the earth. Some of the energy is reflected back into space.Some of the energy is reflected back into space.

Greenhouse GasesGreenhouse Gases trap heat that would leave the atmospheretrap heat that would leave the atmosphere.. HH22OO, , CHCH44, and , and COCO22 are common greenhouse are common greenhouse

gases.gases. ““Global WarmingGlobal Warming” ”

Theory that increasing levels of Greenhouse Theory that increasing levels of Greenhouse gasses is causing the global average temps to gasses is causing the global average temps to increase.increase.

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Bires, 2007 Slide 6

The Ozone Layer (The Ozone Layer (OO33)) Ozone isOzone is

a corrosive poisona corrosive poison in the in the TroposphereTroposphere (where we (where we live) live)

frequently created and given off from free frequently created and given off from free electrical ionization.electrical ionization.

OzoneOzone Absorbs harmful Ultraviolet (UV) energy Absorbs harmful Ultraviolet (UV) energy in the in the

stratospherestratosphere, 11km (6 miles) above us., 11km (6 miles) above us. Note: the Ozone layer is less than 1mm Note: the Ozone layer is less than 1mm

thick!thick! It is always moving, like a cloud, due to It is always moving, like a cloud, due to

weather patterns and climate variations.weather patterns and climate variations.

Page 778 for more info

Stratospheric Ozone.mov

CFCs and Ozone catalyst reaction.mov

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Bires, 2007 Slide 7

Pascal’s Principle and PressurePascal’s Principle and Pressure

French physician, French physician, Blaise PascalBlaise Pascal, showed , showed thatthat fluids fluids (including gasses)(including gasses) exert a uniform exert a uniform

pressure on all the surfaces that they contact.pressure on all the surfaces that they contact. Exerting a Exerting a forceforce on the top surface of a gas, on the top surface of a gas,

causes that force (pressure) to be exerted on causes that force (pressure) to be exerted on all the walls of its container.all the walls of its container.

Pressure is due to the particles of a gas striking Pressure is due to the particles of a gas striking a surfacea surface. We can detect pressure from billions . We can detect pressure from billions upon billions of gas molecules striking a surface upon billions of gas molecules striking a surface at any point in time.at any point in time.

aFp / F = Force

a = area

Which exerts a greater pressure?

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Bires, 2007 Slide 9

Pressure units…Pressure units… The The SI unitSI unit of pressure is the of pressure is the PascalPascal, , PaPa, ,

equaling one newton per square meter.equaling one newton per square meter. Earth’s air pressure at sea level ~ Earth’s air pressure at sea level ~ 100,000 Pa100,000 Pa. .

100kPa100kPa PSIPSI (US) (US)

Pound per square inchPound per square inch. Atmospheric pressure at . Atmospheric pressure at sea level is about sea level is about 14.5 PSI14.5 PSI..

mmHg mmHg (EU, Asia) (AKA: (EU, Asia) (AKA: TorrTorr)) Millimeters of mercuryMillimeters of mercury. . Atmospheric pressure is Atmospheric pressure is 760 mmHg760 mmHg at sea level. at sea level. This has to due with the height of a column of This has to due with the height of a column of

liquid mercury raised in a barometer.liquid mercury raised in a barometer. inHginHg

Inches of mercuryInches of mercury. . Used only in meteorologyUsed only in meteorology.. Atmospheric pressure is apx Atmospheric pressure is apx 30inHg30inHg..

Manometer.swf

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Bires, 2007 Slide 10

And finally…And finally… And, finally…the And, finally…the atmosphere, atmatmosphere, atm

the pressure exerted by the atmosphere at the pressure exerted by the atmosphere at sea level, at 0sea level, at 000C. (This creates STP…)C. (This creates STP…)

SStandard tandard TTemperature and emperature and PPressure:ressure: STPSTP

usually used when referring to usually used when referring to reactions with gases. STP is defined as:reactions with gases. STP is defined as:

1 atm1 atm and 273.15 K and 273.15 K 101 kPa101 kPa and 273.15 K and 273.15 K 760 mmHg760 mmHg and 273.15 K and 273.15 K

When doing work with gases, select the STP that matches the pressure you are using. (atm in this class)

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Bires, 2007 Slide 12

Charles’ LawCharles’ Law French chemist, Jacque French chemist, Jacque

Charles, showed that at Charles, showed that at constant pressureconstant pressure,, temperature and temperature and

volume varied volume varied proportionallyproportionally. That . That is…is…

V / T=kV / T=k (k = some constant #)(k = some constant #)

We tend to write We tend to write Charles’ Law as the Charles’ Law as the volumes and volumes and temperatures under temperatures under two conditions:two conditions:

2

2

1

1

T

V

T

V

Simulation. constant volume

c 1780’s

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Bires, 2007 Slide 13

Boyle’s LawBoyle’s Law A young, adventurous, British aristocrat A young, adventurous, British aristocrat

named Robert Boyle found thatnamed Robert Boyle found that when when temperature is kept constanttemperature is kept constant, volume , volume

varies varies inverselyinversely proportional with pressure proportional with pressure. . That is: That is:

P V = kP V = k (constant) (constant) We tend to write Boyle’s Law as the We tend to write Boyle’s Law as the

volumes and pressures under two volumes and pressures under two conditions:conditions:

2211 VPVP

We’re leaving one law out… can you guess what it is?

c 1660’s

Boyles Law.mov

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Bires, 2007 Slide 14

Charles’ LawCharles’ Law + + Boyle’s Boyle’s LawLaw + + Avogadro’s LawAvogadro’s Law

==THE IDEAL GAS LAWTHE IDEAL GAS LAW

RR is the “ is the “gas constantgas constant” and numerically ” and numerically depends upon the pressure units used.depends upon the pressure units used.

nRTPV Pressure

Volume

(in Liters)

Moles Constant

Temperature

(in Kelvin)

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Bires, 2007 Slide 16

The Gas ConstantThe Gas Constant The Gas Constant is the numerical bridge The Gas Constant is the numerical bridge

between number of moles of a gas, its between number of moles of a gas, its temperature, and volume or pressure.temperature, and volume or pressure.

RR = = 8.3148.314 L L٠٠kPakPa / mol / mol٠٠KK RR = = 0.08210.0821 L L٠٠atmatm / mol / mol٠٠KK

Note that the first constant is in KILO Note that the first constant is in KILO Pascals. When given Pascals, Pascals. When given Pascals, you must you must first convert to kilopascalsfirst convert to kilopascals..

Our calculations will be done in AtmOur calculations will be done in Atm

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Bires, 2007 Slide 17

Dalton’s Law of Partial Dalton’s Law of Partial PressuresPressures

The total pressure in a system is the sum The total pressure in a system is the sum of the individual pressures exerted by each of the individual pressures exerted by each gasgas..

So, if gas So, if gas AA exerts a pressure of exerts a pressure of 2 units2 units, , and gas and gas BB exerts a pressure of exerts a pressure of 3 units3 units, the , the total pressure of a system of equal parts of total pressure of a system of equal parts of A and B, would be ?A and B, would be ?

TotalTotal == A A + + BB ……..…….. 22 + + 33 = = 5 units5 units.. In our atmosphere, In our atmosphere, OxygenOxygen is about is about 21%21%. .

If we have a sample of air at If we have a sample of air at 1 atm1 atm, what is , what is the pressure due to oxygen?the pressure due to oxygen?

PartialPressures.swf

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Bires, 2007 Slide 18

Graham’s Law of Gas EffusionGraham’s Law of Gas Effusion

EffusionEffusion motion of a gas through an openingmotion of a gas through an opening in a in a

container.container. notnot DiffusionDiffusion - - dispersing from higher dispersing from higher

concentration to lower concentrationconcentration to lower concentration.. Rates (speeds) of effusionRates (speeds) of effusion are related to are related to

the the molar massmolar mass of a gas. of a gas. The higher the molar mass, the slower the The higher the molar mass, the slower the

gas will effusegas will effuse.. This is a property of real gasesThis is a property of real gases

Diffusion of Bromine Vapor.MOV

DiffusionandEffusion.swf

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Bires, 2007 Slide 19

Graham’s Law of Gas EffusionGraham’s Law of Gas Effusion

At the same temperature…At the same temperature… The higher the molar mass, the slower the gas The higher the molar mass, the slower the gas

will effusewill effuse.. Graham’s Law of Effusion:Graham’s Law of Effusion:

2

212

21

BBAA vmvm Gas A vs Gas B

Molar mass

Molar mass

velocity

velocity

221 mvKE

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Bires, 2007 Slide 20

Vapor PressureVapor Pressure All liquids exert a vapor pressure.All liquids exert a vapor pressure.

Vapor pressure = liquid’s molecules Vapor pressure = liquid’s molecules gas gas phasephase..

Higher temperatures Higher temperatures greater molecular greater molecular speed speed greater vapor pressure greater vapor pressure..

MoreMore volatile liquidsvolatile liquids exert a greater vapor exert a greater vapor pressure than do less volatile liquidspressure than do less volatile liquids.. Can you explain why this is?Can you explain why this is?

In lab:In lab: we collect gasses over water. we collect gasses over water. There is a small amount of water vapor There is a small amount of water vapor in our gas samples, due to water’s vapor in our gas samples, due to water’s vapor pressure. pressure.

Page 324

Vapor Pressure vs Temperature.mov

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Bires, 2007 Slide 21

Phase DiagramsPhase Diagrams Phase diagramsPhase diagrams

predict if a substance will be a solid, liquid or gaspredict if a substance will be a solid, liquid or gas depends upon the pressure and temperature of the depends upon the pressure and temperature of the

substancesubstance.. Triple PointTriple Point

point where solid, liquid, and gas all exist – point where solid, liquid, and gas all exist – for waterfor water, , 0000CC..

Example on page 381

Notice, that as you increase pressure, the boiling point of water increases-this is why a pressure cooker works.

What about Denver, the “mile-high city?”

End of Gases lecture, Chapters 10,11, problems following

PhaseDiagram.swf

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Bires, 2007 Slide 22

In-chapter problems:In-chapter problems: Page 327, Page 327, #5,7,8#5,7,8 What is Pressure?What is Pressure? Page 327, Page 327, #11-14#11-14 Pressure UnitsPressure Units Page 327, Page 327, #17-19#17-19 Pressure ConversionsPressure Conversions Page 330, Page 330, #20-24e#20-24e Boyle’s LawBoyle’s Law Page 330, Page 330, #25-27#25-27 Charles’ LawCharles’ Law Page 330, Page 330, #31-35o#31-35o Combined LawCombined Law Page 331, Page 331, #39,40#39,40 Dalton’s Law of Partial Dalton’s Law of Partial

PressuresPressures Page 357, Page 357, #9-13o#9-13o Avogadro’s Molar GassesAvogadro’s Molar Gasses Page 358, Page 358, #17-20#17-20 Ideal Gas LawIdeal Gas Law Page 358, Page 358, #23-29o#23-29o Ideal Gas Law and Ideal Gas Law and

StoichiometryStoichiometry Page 359, Page 359, #39-42#39-42 Graham’s Law of Gas EffusionGraham’s Law of Gas EffusionEnd of Gases Unit, Chapters 10,11

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Bires, 2007 Slide 23

CCSD Syllabus ObjectivesCCSD Syllabus Objectives 11.1: Kinetic Molecular Theory11.1: Kinetic Molecular Theory 11.2: Physical Properties of Gasses11.2: Physical Properties of Gasses 11.3: STP11.3: STP 11.4: Volume-Temp relationships11.4: Volume-Temp relationships 11.5: Volume-Pressure relationships11.5: Volume-Pressure relationships 11.6: Density-Volume-Pressure-Temperature11.6: Density-Volume-Pressure-Temperature 11.10: Ideal Gas Law11.10: Ideal Gas Law 11.11: Graham’s Law11.11: Graham’s Law 11.12: Ideal Gas vs Real Gas11.12: Ideal Gas vs Real Gas 12.3: Evaporation, Condensation, 12.3: Evaporation, Condensation,

SublimationSublimation 21.1: Environmental Chemistry21.1: Environmental Chemistry