Chapter #11
Molecular Composition
of Gases
Chapter 11.1
• Gay-Lussac’s law of combining volumes of
gases states that at constant temperature
and pressure, the volumes of gaseous
reactants and products can be expressed
as ratios of small whole numbers.
• Avogadro’s law states that equal volumes
of gases at the same temperature and
pressure contain equal numbers of
molecules.
• Standard Molar Volume of a gas is the
volume occupied by one mole of a gas at
STP.
• 1 mole = 22.4 L
Chapter 11.2
The ideal gas law
PV=nRT
Temperature must be in Kelvin!!!
R is the gas constant
62.4 or 0.0821 you have to use the units of
Pressure to pick which one…
So… if pressure is in mmHg R=62.4
If pressure is in atm R= 0.0821
Molar mass or Density
M= mRT
PV
D= MP
RT
M= DRT
P
M= Molar Mass
m= mass in grams
R= gas constant
T= Kelvin Temperature
P= Pressure
V= Volume
D= Density
Chapter 11.3
• Stoichiometry of Gases
• Volume to volume calculations
• Liter to Liter same as Mole to Mole
Mole to mole ratio from
balanced equation
• Given # of
Liters
x
what you want
what you have
=
Liters of
what you
want
Chapter 11.4
• Graham’s law of Effusion states that the rates of
effusion of gases at the same temperature and
pressure are inversely proportional to the square
roots of their molar masses.
• A is the lighter gas, B is the heavier one.
Work Cited
• “Cartoon”. August 11, 2006.
http://www.sapphireblue.com/catgoddess/farside
.gif
• “Gay-Lussac’s Law”. February 13, 2007.
http://www.pinkmonkey.com/studyguides/subject
s/chem/chap6/c0606501.asp
• “Avogadro’s Law”. February 13, 2007.
http://www.chem.ufl.edu/~itl/2045/matter/FG10_
010.GIF
• “Grahams Law”. February 15, 2007.
http://www.humboldt.edu/~rap1/ChemSupp/Equ
ations/EffusRatio.gif