1 Chapter 12: Gases and Chapter 12: Gases and Their Properties Their Properties
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Chapter 12: Gases and Their Chapter 12: Gases and Their PropertiesProperties
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Properties of GasesProperties of Gases
Gases form homogeneous mixtures Gases are compressible All gases have low densities
air 0.0013 g/mL water 1.00 g/mL iron 7.9 g/mL
Gases expand to fill their containers uniformly A gas exerts a pressure
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Kinetic Molecular TheoryKinetic Molecular Theory Gases consist of molecular particles moving in straight
lines at any given instant. Molecules collide with each other and the container
walls without any net loss of energy. Gas molecules behave independently --
attractive/repulsive forces between them are negligible. Gas molecules are widely spaced, the actual volume of
molecules is negligible compared to the space they occupy.
The average kinetic energy of the gas particles is proportional to the temperature.
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Kinetic GraphKinetic Graph
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Pressure, Volume, and Temperature Pressure, Volume, and Temperature RelationshipsRelationships
A. Pressure, volume, and temperature unitsB. Boyle's lawC. Charles' lawD. Gay-Lussac's lawE. Avogadro's law
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Pressure =
-measured with barometer or manometer
forceunit area
SI: 1 pascal (Pa) = 1 N/m2
common: 1 atm = 760 mm Hg= 760 torr= 14.7 lb/in2 (psi)= 101.325 kPa= 1.013 bar
Volume: mL, LTemperature: K
A. Pressure, Volume, and A. Pressure, Volume, and Temperature RelationshipsTemperature Relationships
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PressurePressure
Defined as force per unit area
skilopascalmsec
kg
m
)(kg)(m/sec
distance
onacceleratimass
Area
ForcePressure
22
2
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Atmospheric pressureAtmospheric pressure
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BarometerBarometer
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ManometersManometers
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Pressure UnitsPressure Units
101.325 kPa = 760 mmHg=760 torr=1 atm=30 in Hg=14.7 psi
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Robert Boyle, 1662: for a sample of gas at constant T, V 1/P
V = or PV = constant
P1V1 = P2V2 (at constant T)
constantP
B. Boyle’s lawB. Boyle’s law
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Boyles LawBoyles Law
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Jacques Charles, 1787: for a sample of gas at constant P, V T (K)
V = constant x T or = constant
VT
V1
T1
V2
T2
= (at constant P)
C. Charles’ lawC. Charles’ law
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Charles LawCharles Law
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Joseph Gay-Lussac, ~1800: for a sample of gas at constant V, P T (K)
P = constant x T or = constant
PT
P1
T1
P2
T2
= (at constant V)
D. Gay-Lussac’s lawD. Gay-Lussac’s law
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E. Avogadro’s lawE. Avogadro’s law
Amadeus Avogadro, 1811: at constant T and P, V n
V = constant x n or = constant
Vn
V1
n1
V2
n2
= (at constant T & P)
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Since PV = constant, P/T = constant, V/T = constant, and V/n = constant
= constant, R (universal gas constant)
or PV = nRT
PVnT
The Ideal gas lawsThe Ideal gas laws
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STP: 0ºC (273 K) and 1.00 atm (760 torr)molar volume = average volume occupied by one mole of gas at STP
= 22.4 L/mol
R = =
= 0.0821 L·atm/mol·K= 6.24 x 104 mL·torr/mol·K
PVnT
(1.00 atm)(22.4 L)(1.00 mol)(273 K)
STP and molar volumeSTP and molar volume
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mw =
since n = mw =
and since d = mw =
e.g., If one finds that a 0.108-g sample of gas occupies a volume of238 mL at 25ºC and 525 torr, what is the molecular weight of the gas?
mn
PVRT
mRTPV
mV
dRTP
Gas densities and molar massGas densities and molar mass
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partial pressure, p = pressure exerted by each gas in a mixture of gases
i
itotal pP
e.g., If 6.00 g of O2 and 9.00 g of CH4 are placed in a 15.0-L containerat 0º, what is the partial pressure of each gas and the total pressure inthe container.
Dalton’s law of partial pressuresDalton’s law of partial pressures 1. Dalton’s law1. Dalton’s law
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PT = p1 + p2 + p3…
1 gas offraction mole ,/
/1
T
1
T
1
T
1 Xn
n
VRTn
VRTn
P
p
p1 = X1PT
e.g., Air is 78 mol % N2 and 22 mol % O2. What is the partial pressureof each gas if the atmospheric pressure is 713 torr?
Dalton’s law of partial pressuresDalton’s law of partial pressures 2. mole fraction2. mole fraction
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vapor pressure = pressure exerted by evaporation of a liquid (or sublimation of a solid)
vacuum
liquidor solid
equilibriumat some T
pvap
pvap increases with T
e.g., H2O T pvap
0ºC 4.6 torr 25ºC 23.8 torr100ºC 760 torr (boils!)
Dalton’s law of partial pressuresDalton’s law of partial pressures3. collecting gases over water3. collecting gases over water
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Mixture of gas and water vapor.
PT = pgas + pvap(H2O)
Dalton’s law of partial pressuresDalton’s law of partial pressures3. collecting gases over water3. collecting gases over water
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Mole FractionMole Fraction
))(P(XP
andmoles total
component of moles(X)fraction Mole
total11