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GasesChapter 5
Properties of gases and gas laws.
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What does this show about gases?Why?
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Kinetic Molecular Theory
The KMT explains what happens to gases on a molecular level and assumesthat
1. Gas particles are point masses (have negligible volumesince the distance between molecules is !"# greater.
$. The particles are in rapid% random% constant straight linemotion. "ll collisions are perfectl& elastic (no energ& is lost.
'. There are ) attractive or repulsive forces betweenparticles.
*. The average +inetic energ& is directl& proportional totemperature according to the e,uation
K-avg/mu$
where u$average mean s,uare speed '#T0M
molar mass
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Temperature and Molecular Speed
Higher
temperature
will shift
average
molecular
speed to the
right
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Physical Characteristics of Gases
Gases have high +inetic energ& and
a. have no definite volume or shape
(compressible.
b. assume the shape and volume of their
containers.
c. there is much space betweenmolecules (ver& low densit&.
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What is pressure?
Pressure is a force per unit area. !or gases%pressure comes from the pounding ofmolecules against each other and the walls of
the container.2hat will affect pressure3 4ncreasing temperature and concentration will
increase pressure% and decreasing volume(s,uee5ing will increase pressure.
6-M) 2hat causes pressure in theatmosphere3 2h& doesn7t water in a test tubefall out when inverted3
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ow is pressure measured?
"tmospheric pressure is measured with a
barometer.
2h& is mercur& used3 8impl& because it has a
high densit& (1'.9 g0m:% so the barometer can
be small.Which gas has the
highest pressure? How
would the tubes look if
the gases inside were at
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Gas pressure using a manometer
" manometer is used to measure pressure of
gases other than at atmospheric pressure.
CASE 1 gaspressure e!uals
atm pressure"#gas
$ #atm%
CASE & gaspressure is greater
than atm pressure"#gas$ #atm ' #h%
CASE ( gaspressure is less
than atm pressure"#gas$ #atm ) #h%
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Temperature and Pressure ofGases
The average +inetic energ& of all the
molecules is proportional to the temperature.
Pressureis the force of the collisionsbetween the gas particles and the sides of the
container.
The volume of a gas(!% the number of gasparticles in that volume(n% the pressure of
the gas(P% and the temperature of the gas(T
are variables that depend on one another.
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Standard Temperature andPressure of Gases
8tandard atmospheric pressure
"#"$%&5 'Pa ( " atm ( )*# torr ( )*# mm g
8tandard temperature #+C ( &)% K
2e indicate that a gas has been measured
at standard conditions b& the capital lettersSTP(standard temp. and atm. pressure
E*periments show that at S+#, 1 mole of an
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Pressure ,nits and Con-ersions
There are four different units of pressure
used in chemistr&. ;ere the& are
1 atmospheres (atm$ millimeters of mercur& (mm;g
' Torr
* +iloPascals (+Pa
1 atm = 101.3 kPa = 760.0 mmHg = 760.0 torr
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Sample Problems.
-x
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Con-erting /etween ,nits ofTemperature
A -B-#C T-MP-#"TD#- D8-6 4 "G"8 :"2
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/oyle1s 2aw
#obert Eo&le% a
Eritish chemist%examined the
relationship between
volumeand pressureof gases.
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/oyle1s 2aw
If the amount (n)
and the
temperature (T) ofa gas remain
constant, the
pressure exerted
by the gas varies
inversely as the
volume.
Hg
added,
pressureincr-
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/oyle1s 2aw
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3pplying /oyle1s 2aw
-x " gas is collected and found to fill $.?= :
at $*= +Pa. 2hat will be its volume at
standard pressure34solate B$ P1B1 P$B$
P1B1 P$B$
P$ P$
P1B1 B$
P
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Charles1s 2aw
Jac,ues
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Charles1s 2aw
The volume of a
quantity of a gas,held at a constant
pressure, varies
directly with the
elvin
temperature.
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Charles1s 2aw
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Charles1s 2aw and 3bsolute 7ero
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,sing Charles1s 2aw8 we can
deri-e the following e9uation.
!"
:T"
( !&
:T&
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3pplying Charles1s 2aw
-x" gas is collected and found to fill $.?=
: at $=.>
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More Charles1s Problems constant P6
1*.*> : of a gas is collected at =>.>>. K
' >: at $>.> < is compressed to 1.>> :.
"8 1*@ K
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,sing the Combined Gas 2aw.
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Combined Gas 2aw Problems
"6 3 gas has a -olume of ;##$# m2 at minus &%$## +Cand %##$# torr$ What would the -olume of the gas beat &&)$# +C and *##$# torr of pressure?
3>S. ;##$ m2
&6 5##$# liters of a gas are prepared at )##$# mm g and#$# +C$ The gas is placed into a tan' under highpressure$ When the tan' cools to $# +C8 thepressure of the gas is %#$# atm$ What is the -olume ofthe gas?
3>S. =$5" 2
%6 The pressure of a gas is reduced from "#$# mm gto ;5#$# mm g as the -olume of its container isincreased by mo-ing a piston from ;5$# m2 to %5#$#m2$ What would the final temperature be if theoriginal temperature was =#$# +C?
3>S. "#*# K
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3-ogadro1s 2aw
The volume of a gas
maintained atconstant temperature
and pressure is
directly proportional
to the number of
moles of the gas.
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Dsing "vogadro7s :aw% we can derive the
following e,uation
!":n"( !&:n&
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So, what is the volume for an8 gas at S+#? &&-. /9mol:
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,sing 3-ogadro1s 2aw
-x " balloon isfilled with $.>moles of ;elium
gas% occup&ing**.? : at constanttemp. ;ow man&liters will beoccupied if thenumber of molesis reduced to 1.=3
4solate un+nown
B10n1 B$0n$
B$ n$B10n1
**.? : x 1.= mol
$.> mol
''.9 :
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The deal Gas @9uation
2hen we combine Eo&le7s%
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,sing the deal Gas 2aw.
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More deal Gas Problems
1 " sample of mol
$ " flashbulb contains $.* x1>*moles of )$
gas at a
pressure of $.>1 +Pa and a temperature of 1I
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Calculating Bensity and Molar Mass
2e can use the ideal gas e,uation to
calculate gas densit&.
6ensit& has the units g0: so we rearrange thee,uation to
n LPL
B #Tow the units on the left are moles0: so we
can multipl& each side m& molar mass (units
g0mole..
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nM PM
B #T
moles cancel leaving units of g0:(densit&.
Thus% ddensity6 ( PM
AT#earranged% M molar mass6 ( dAT
P
C l l t th d iti f > d t
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Calculate the densities of >&and e at
STP4using the gas density e9uation.
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Bensity and Molar Mass Problems
2hat is the densit& of carbon tetrachloride vapor
at @1* torr and 1$=.?$I g0:
2hat is the molar mass of a substance that has adensit& of $.== g0: at a pressure of @?= torr and
temperature of *=
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Balton s 2aw ofPartial Pressures
)ur calculations so far have been for pure
gases. John 6alton formed a h&pothesis about
pressure exerted b& a mixture of gases.
6alton7s :aw of Partial Pressure The total
pressure in a container is the sum of the partial
pressures of all the gases in the container.
Ptotal( P"0 P&0 P%4
' $'
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;alton
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Consider a case in which two gases, Aand =, are in a
container of volume >-
PA$nA+
V
P=$nB+
V
nAis the number of moles of A
n=is the number of moles of =
P+$PA'P= XA$nA
nA' n=
X=$n=
nA' n=
PA$xAP+ P=$x=P+
Pi$xiP+
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Gas Mi
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Partial Pressure of 3ir
"ir is an example of a mixture of gases.
nitrogen is @?.>?* ox&gen is $>.I*?
argon is >.I'*
carbon dioxide is >.>'1=
neon% helium% +r&pton% and xenon are
among the other trace gases.
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Gases in air
Wh t i th ti l f
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What is the partial pressure ofo torr. 4f @? of air is nitrogen%
then @? of pressure is due to nitrogenmolecules.
>.@? x @9> torr =I' torr
$1 of air is ox&gen so $1 of pressureis due to ox&gen molecules.
>.$1 x @9> torr 19> torr
C ll ti G b W t
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Collecting Gases by WaterBisplacement
)ne method to collect gases is b& water
displacement.
Gases must be insoluble in water.2hen collection is complete% water vapor
is present in the collection container and
must be accounted for in the partialpressures of gases.
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&@Cl( "s% &@Cl "s% ' (& "g%
Bottle full of oxygen gas and water vapor
P+ $P 'PH &&
d t f
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ow do you correct for -aporpressure of water?
Bolume of a dr& gas
Pgas( Ptotal Pwater
-x " ,uantit& of gas is collected over
water at ?< in a >.'=' : vessel at ?*.=
+Pa. 2hat volume would the dr& gas
occup& at standard atmosphericpressure and ?
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Continued4
P1B1 P$B$
P1B1 B$
P$
?'.* +Pa x >.'=' : $I1 :
1>1.' +Pa
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Partial Pressure Practice Problem
" gas is collected over water and occupies a
volume of =I9 cm'at *'1.1 +Pa. 2hat volume will the dr& gas occup&
at *'< and standard atmospheric pressure3 Thevapor pressure of water at *'< is ?.9 +Pa.
"8 =*= m:
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Biffusion and Graham1s 2aw
Kinetic theor& states that molecules travel in
straight lines. Molecules often collide with other
molecules which alters its path and sends it on
another straight path. This is the basic idea of diffusion. "s gas
molecules diffuse% the& become more and
more evenl& distributed throughout theircontainer. http00highered.mcgrawhill.com0sites0>>@$*I=?==0studentLview>0chapter$0animationLLhowLdiffusio
http://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.htmlhttp://highered.mcgraw-hill.com/sites/0072495855/student_view0/chapter2/animation__how_diffusion_works.html8/13/2019 5. AP Chapt 5 Gases
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ow is effusion different from
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ow is effusion different fromdiffusion?
Aelationship between mass and
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Aelationship between mass andrate of diffusion
Dsing Graham7s :aw% we can derive
r" ( DM&D
r&
M"
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Be-iations from deal Gas /eha-ior
2hen using the ideal gas e,uation% two
assumptions were made
1. Gas particles have novolume.$. Gas particles have noattractive forces
between them.
2e will now examine how real gases candeviate from these assumptions.
ow are real gases different from ideal?
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ow are real gases different from ideal?
"ssumption 1 Gases occup& no volume. "t low pressures% both ideal and real gases
are far apart% separated b& empt& space. "s pressure is applied% real gases begin to
ta+e up more of the empt& space. 4dealgases are still far apart.
"n ideal gas can have 5ero volume% but areal gas will become a li,uid underincreased pressure.
ow are real gases different from ideal?
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"ssumption $ Gases have no attractive forcesbetween them.
4f gases are made up of polar molecules such
as water% the attractive forces are large and thebehavior of this real gas is mar+edl& differentfrom an ideal gas.
There are even wea+ attractive forces(dispersion forces between noble gases.
!or most gases% the ideal gas laws areaccurate to about 1.
ow are real gases different from ideal?
What does this show about the effect of intermolecular forces on the
t d b
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pressure e*erted b8 a gas-
;eviations from deal =ehavior
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no gas behaves ideall8- =ehavior becomes
less ideal at high pressures
1 mole of ideal gas
PV$ nRT
n =PV
RT$ 1-3
epulsive Dorces
Attractive Dorces
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Scuba Chemistry.
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Scuba Chemistry.The /ends
"s divers sin+ down to high pressure water (pressure
doubles at 1> m or '' ft% the air that the& breathe
becomes more soluble in their blood.
6ecompression sic+ness% or Nthe bendsO occurs asdivers rise to the surface% the pressure decreases% and
bubbles of gas suddenl& form in the bloodstream as
the gas becomes less soluble.
6ecompression sic+ness% also +nown as the bends% is
one danger of diving. )ther dangers include nitrogen
narcosis% ox&gen toxicit& and simple drowning (if &ou
run out of air before ma+ing it bac+ to the surface.
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Barwin 3ward Winner "===4+he Asaka =eer corporation brews Suiso brand beer, in which the carbon
dio*ide normall8 used to add fi77 has been replaced b8 the more
environmentall8 friendl8 h8drogen gas- +wo side effects of the h8drogen gas
have made the beer e*tremel8 popular at karaoke sing)along bars and clubs-
Dirst, because h8drogen molecules are lighter than air, sound waves are
transmitted more rapidl8, so individuals whose lungs are filled with the
nonto*ic gas can speak with an uncharacteristicall8 high voice- E*ploiting this
!uirk of ph8sics, chic urbanites can now sing soprano parts on karaoke sing)
along machines after consuming a big gulp of Suiso beer-
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CE& emissions
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ncoming Solar Aadiation
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Greenhouse Gases A Spectra
"tmospheric
gases that
trap infrared
heat.
THE END
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THE END
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WarmFup. What1s the o'e?
8everal &ears ago% a scientific publication reported
that one of their readers% while attending a
scientific conference% overheard two colleagues
discussing a paper that had been presented. 4n allseriousness% one said to the other something to
the effect that% N;e reported that the internal
temperature of the 8un was about 1= million
degrees% but 4 don7t remember whether that was in&E6 and
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Warm up. f laughing gas >&E6 andC> were released4$