Behavior of Gases
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Behavior of Behavior of GasesGases
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Airbags fill with NAirbags fill with N22 gas in an accident. gas in an accident.
Gas is generated by the decomposition of sodium azideGas is generated by the decomposition of sodium azideGas molecules save your life! Gas molecules save your life!
2 NaN2 NaN33 ---> 2 Na + 3 N ---> 2 Na + 3 N22
Example of Importance of GasesExample of Importance of Gases
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Kinetic Molecular Theory (KMT)Kinetic Molecular Theory (KMT)
Particles in an Particles in an ideal gasideal gas……have no volume.have no volume.have elastic collisions. have elastic collisions. are in constant, random, straight-line motion.are in constant, random, straight-line motion.don’t attract or repel each other.don’t attract or repel each other.have an avg. KE directly related to Kelvin have an avg. KE directly related to Kelvin
temperature.temperature.
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Real GasesReal Gases
Particles in a Particles in a REAL gasREAL gas…… have their own volumehave their own volume attract each otherattract each other
Gas behavior is Gas behavior is most idealmost ideal…… at low pressuresat low pressures at high temperaturesat high temperatures when very small in sizewhen very small in size when nonpolarwhen nonpolar
PLIGHTPLIGHT
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Characteristics of GasesCharacteristics of GasesGases expand to fill any container uniformly.Gases expand to fill any container uniformly.
Are in random motion, have no attractionAre in random motion, have no attraction
Gases have very low densities.Gases have very low densities.Particles have no volume = lots of empty spaceParticles have no volume = lots of empty space
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Characteristics of GasesCharacteristics of Gases There is a lot of “free” space in a gas.There is a lot of “free” space in a gas.
Gases can be compressed.Gases can be compressed.no volume = lots of empty spaceno volume = lots of empty space
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Gases undergo diffusion & effusion.Gases undergo diffusion & effusion.Are always in random motionAre always in random motionSmaller and lighter gas particles do this fasterSmaller and lighter gas particles do this faster
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Gas PressureGas Pressure
area
forcepressure
Which shoes create the most pressure?
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What Causes Pressure?What Causes Pressure?http://www.chm.davidson.edu/vce/http://www.chm.davidson.edu/vce/
kineticmoleculartheory/Pressure.htmlkineticmoleculartheory/Pressure.html
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Factors Affecting Gas PressureFactors Affecting Gas Pressure
Number of MolesNumber of Moles (Amount of gas) (Amount of gas)As # of particles increase, the number of As # of particles increase, the number of
collisions with the container wall increases.collisions with the container wall increases.
VolumeVolumeSmaller the volume, the greater the pressure Smaller the volume, the greater the pressure
exerted on the container.exerted on the container.
TemperatureTemperatureAs temp. increases, KE increases, this increases As temp. increases, KE increases, this increases
frequency of collisions making pressure frequency of collisions making pressure increase.increase.
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Measuring Gas PressureMeasuring Gas PressureBarometerBarometer
measures atmospheric pressuremeasures atmospheric pressure (developed by Torricelli in 1643)(developed by Torricelli in 1643)
Mercury BarometerAneroid Barometer
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Standard Pressure (Sea Level)Standard Pressure (Sea Level)
101.3 kPa (kilopascal)101.3 kPa (kilopascal)
1 atm 1 atm
760 mm Hg (also called torr)760 mm Hg (also called torr)
You may be asked to convert between units of pressure!You may be asked to convert between units of pressure!
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Hg rises in tube until force ofHg rises in tube until force ofHg (down) balances the forceHg (down) balances the forceof atmosphere (pushing up). of atmosphere (pushing up).
(Just like a straw in soft drink)(Just like a straw in soft drink)
Column height measuresColumn height measurespressure of atmospherepressure of atmosphere
1 standard atmosphere (atm) 1 standard atmosphere (atm) = 760 mm Hg (or torr) = 760 mm Hg (or torr)
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Measuring Gas PressureMeasuring Gas PressureManometerManometer
measures contained gas pressuremeasures contained gas pressure
U-tube Manometer
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Working Working withwith
FormulasFormulas
The Gas LawsThe Gas Laws
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TemperatureTemperature
ºC
K
-273 0 100
0 273 373
K = ºC + 273
Always use absolute temperature (Kelvin) Always use absolute temperature (Kelvin) when working with gases.when working with gases.
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Gas properties can be modeled using math.Gas properties can be modeled using math.Model depends on:Model depends on:
V = volume of the gas (L)V = volume of the gas (L)
T = temperature (K)T = temperature (K)ALL temperatures MUST be in Kelvin!!! ALL temperatures MUST be in Kelvin!!!
n = amount (moles)n = amount (moles)
P = pressure (atmospheres or kPa)P = pressure (atmospheres or kPa)
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Standard Temperature & PressureStandard Temperature & Pressure
0°C 1 atm
273 K 101.325 kPa
760 mmHg
-OR-
STP
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Boyle’s LawBoyle’s Law
The pressure and volume of a The pressure and volume of a gas are inversely related gas are inversely related at constant mass & tempat constant mass & temp
P
V
PV = k
Robert Boyle Robert Boyle (1627-1691). Son (1627-1691). Son of Earl of Cork, of Earl of Cork, IrelandIreland..
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Boyle’s Law
Since P x V is always a constant:
P1 x V1 = P2 x V2
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Pressure and Volume Relationshiphttp://www.chm.davidson.edu/vce/kineticmoleculartheory/PV.html
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If Mass and Temp are ConstantIf Mass and Temp are Constant
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Boyle’s LawBoyle’s Law
Balloon in a Vacuum
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kT
VV
T
Charles’ LawCharles’ Law
The volume and absolute The volume and absolute temperature (K) of a gas are temperature (K) of a gas are directly related directly related at constant mass & pressureat constant mass & pressure
Jacques Charles Jacques Charles (1746-1823). Isolated (1746-1823). Isolated boron and studied boron and studied gases. Balloonistgases. Balloonist..
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Charles’ Law
Since V/T is always a constant:
V1 = V2
T1 T2
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If Mass and Pressure are ConstantIf Mass and Pressure are Constant
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Charles’ LawCharles’ Law
http://group.chem.iastate.edu/Greenbowe/sections/projectfolder/flashfiles/gaslaw/charles_law.html
http://www.pinnaclescience.com/demo.htm
Pour Liquid Nitrogen on Balloon!!
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kT
PP
T
Gay-Lussac’s LawGay-Lussac’s Law The pressure and absolute The pressure and absolute
temperature (K) of a gas are temperature (K) of a gas are directly related directly related at constant mass & volumeat constant mass & volume
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Gay – Lussac’s Law
Since P/T is always a constant:
P1 = P2
T1 T2
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Pressure and Temperature RelationshipPressure and Temperature Relationship http://www.chm.davidson.edu/vce/http://www.chm.davidson.edu/vce/
kineticmoleculartheory/PT.htmlkineticmoleculartheory/PT.html
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Review of 3 Gas Laws
Summary of Changing VariablesSummary of Changing Variableshttp://www.mhhe.com/physsci/chemistry/http://www.mhhe.com/physsci/chemistry/essentialchemistry/flash/gasesv6.swfessentialchemistry/flash/gasesv6.swf
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P1V1
T1
=P2V2
T2
P1V1T2 = P2V2T1
The good news is that you don’t have to remember all three gas laws! The good news is that you don’t have to remember all three gas laws! We can combine them into a single equation.We can combine them into a single equation.If you should only need one of the other gas laws, you can cover up the item that is constant and you will get that gas law!
Combined Gas Law (on Ref Table)Combined Gas Law (on Ref Table)
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ExampleExample
Set up Data TableSet up Data Table
PP1 1 = 0.800 atm V= 0.800 atm V11 = .180 L = .180 L T T11 = 302 K = 302 K
PP22 = 3.20 atm V = 3.20 atm V22= .090 L T= .090 L T2 2 = ??= ??
A sample of helium gas has a volume of 0.180 L, a pressure of 0.800 atm and a temperature of 29°C. What is the new temperature (°C) of the gas at a volume of .090 L and a pressure of 3.20 atm?
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GIVEN:
V1 = 473 ml
T1 = 36°C = 309K
V2 = ?
T2 = 94°C = 367K
WORK:
P1V1T2 = P2V2T1
Gas Law ProblemsGas Law ProblemsA gas occupies 473 ml at 36°C. Find its A gas occupies 473 ml at 36°C. Find its
volume at 94°C. volume at 94°C. CHARLES’ LAW
T V
(473 ml )(367 K)=V2(309 K)
V2 = 562 ml
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GIVEN:
V1 = 100. mL
P1 = 150. kPa
V2 = ?
P2 = 200. kPa
WORK:
P1V1T2 = P2V2T1
Gas Law ProblemsGas Law Problems
A gas occupies 100. mL at 150. kPa. Find A gas occupies 100. mL at 150. kPa. Find its volume at 200. kPa. its volume at 200. kPa.
BOYLE’S LAW
P V
(150.kPa)(100.mL)=(200.kPa)V2
V2 = 75.0 mL
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GIVEN:
V1 = 7.84 ml
P1 = 71.8 kPa
T1 = 25°C = 298 K
V2 = ?
P2 = 101.325 kPa
T2 = 273 K
WORK:
P1V1T2 = P2V2T1
(71.8 kPa)(7.84 ml)(273 K)
=(101.325 kPa) V2 (298 K)
V2 = 5.09 ml
Gas Law ProblemsGas Law Problems A gas occupies 7.84 ml at 71.8 kPa & 25°C. A gas occupies 7.84 ml at 71.8 kPa & 25°C.
Find its volume at STP. Find its volume at STP.
P T VCOMBINED GAS LAW
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GIVEN:
P1 = 765 torr
T1 = 23°C = 296K
P2 = 560. torr
T2 = ?
WORK:
P1V1T2 = P2V2T1
Gas Law ProblemsGas Law Problems
A gas’ pressure is 765 torr at 23°C. At A gas’ pressure is 765 torr at 23°C. At what temperature will the pressure be 560. what temperature will the pressure be 560. torr? torr?
GAY-LUSSAC’S LAW
P T
(765 torr)T2 = (560. torr)(309K)
T2 = 226 K = -47°C
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Dalton’s Law of Partial PressuresDalton’s Law of Partial Pressures
PPtotal total == PP11+P+P22+….+….
Total pressure of a mixture of gases in a Total pressure of a mixture of gases in a container is the container is the sum sum of the individual of the individual pressures (pressures (partial pressurespartial pressures) of each gas, ) of each gas, as if each took up the total space alone.as if each took up the total space alone.
This is often useful when gases are This is often useful when gases are collected “over water”collected “over water”
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Dalton’s Law of Dalton’s Law of Partial PressuresPartial Pressures
The total pressure of a mixture of The total pressure of a mixture of gases equals the sum of the partial gases equals the sum of the partial pressures of the individual gases.pressures of the individual gases.
Ptotal = P1 + P2 + ...
Patm = PH2 + PH2O
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GIVEN:
PH2 = ?
Ptotal = 94.4 kPa
PH2O = 2.72 kPa
WORK:
Ptotal = PH2 + PH2O
94.4 kPa = PH2 + 2.72 kPa
PH2 = 91.7 kPa
Dalton’s LawDalton’s Law Hydrogen gas is collected over water at Hydrogen gas is collected over water at
22.5°C. Find the pressure of the dry gas if the 22.5°C. Find the pressure of the dry gas if the atmospheric pressure is 94.4 kPa.atmospheric pressure is 94.4 kPa.
Look up water-vapor pressure on for 22.5°C.
Sig Figs: Round to least number of decimal places.
The total pressure in the collection bottle is equal to atmospheric pressure and is a mixture of H2 and water vapor.
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GIVEN:
Pgas = ?
Ptotal = 742.0 torr
PH2O = 42.2 torr
WORK:
Ptotal = Pgas + PH2O
742.0 torr = PH2 + 42.2 torr
Pgas = 699.8 torr
A gas is collected over water at a temp of 35.0°C when A gas is collected over water at a temp of 35.0°C when the barometric pressure is 742.0 torr. What is the partial the barometric pressure is 742.0 torr. What is the partial pressure of the dry gas? pressure of the dry gas?
DALTON’S LAW
Look up water-vapor pressure for 35.0°C.
Sig Figs: Round to least number of decimal places.
Dalton’s LawDalton’s Law
The total pressure in the collection bottle is equal to barometric pressure and is a mixture of the “gas” and water vapor.
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Graham’s LawGraham’s Law
DiffusionDiffusionSpreading of gas molecules throughout a Spreading of gas molecules throughout a
container until evenly distributed.container until evenly distributed.
EffusionEffusionPassing of gas molecules through a tiny Passing of gas molecules through a tiny
opening in a containeropening in a container
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Graham’s LawGraham’s Law
Speed of diffusion/effusionSpeed of diffusion/effusionKinetic energy is determined by the Kinetic energy is determined by the
temperature of the gas.temperature of the gas.
At the same temp & KE, At the same temp & KE, heavier molecules heavier molecules move more slowlymove more slowly..
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kn
VV
n
Avogadro’s Principle Equal volumes of gases contain
equal numbers of moles at constant temp & pressure true for any gas
Equal volumes of gases at the same T and P have the Equal volumes of gases at the same T and P have the same number of same number of moleculesmolecules..