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Gas Phase Reaction Stoichiometry
Sample Exercise 6.8
Oxygen generators in some airplanes are based on the chemical
reaction between sodium chlorate and iron:
NaClO3(s) + Fe(s) → O2(g) + NaCl(s) + FeO(s)
The resultant O2 is blended with cabin air to provide 10–15 minutes
of breathable air for passengers. How many grams of NaClO3 are
needed in a typical generator to produce 125 L of O2 gas at 1.00
atm and 20.0°C?
Density (d) Calculations
d= m
V
m = the mass of the gas in g
M = the molar mass of the gas
Sample Exercise 6.9
Calculate the density of air at 1.00 atm and 302 K and compare your
answer with the density of air at STP (1.29 g/L). Assume that air has
an average molar mass of 28.8 g/mol. (This average molar mass is
the weighted average of the molar masses of the various gases in
air.)
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Molar Mass (M) of a Gas
Sample Exercise 6.10
Vent pipes at solid-waste landfills often emit foul-smelling gases that
may be either relatively pure substances or mixtures of several gases.
A sample of such an emission has a density of 0.650 g/L at 25.0°C
and 757 mmHg. What is the molar mass of the gas emitted? (Note
that if the sample is a mixture, the answer will be the weighted average
of molar masses of the individual gases.)
Dalton’s Law of Partial Pressures
V and T
are
constant
P1
P2
Ptotal = P1 + P2
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Consider a case in which two gases, A and B, are in a
container of volume V.
PA =
nART
V
nA is the number of moles of A
PB =
nBRT
V
nB is the number of moles of B
PT = PA + PB
Sample Exercise 6.11
Scuba divers who descend more than
45 m below the surface may breathe a
gas mixture that is 11.7% He, 56.2%
N2, and 32.1% O2 by mass. Calculate
the mole fraction of each gas in this
mixture.
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Sample Exercise 6.12
Calculate the partial pressure in atmospheres of O2 in
the air outside an airplane cruising at an altitude of 10
km, where the atmospheric pressure is 190.0 mmHg.
The mole fraction of O2 in the air is 0.210.
Determining The Partial Pressure of a
Gas Collected Over Water
PT = PO2 + PH2 O
Bottle full of oxygen
gas and water vapor
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Sample Exercise 6.13
During the decomposition of KClO3, 92.0 mL of gas is collected by the
displacement of water at 25.0°C. If atmospheric pressure is 756 mmHg,
what mass of O2 is collected?
Kinetic Molecular Theory of Gases
1. A gas is composed of molecules that are separated from
each other by distances far greater than their own
dimensions. The molecules can be considered to be points;
that is, they possess mass but have negligible volume.
2. Gas molecules are in constant motion in random directions.
Collisions among molecules are perfectly elastic.
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3. Gas molecules exert neither attractive nor repulsive
forces on one another.
4. The average kinetic energy of the molecules is
proportional to the temperature of the gas in Kelvins.
KEavg = ½ mu2rms  TKelvin
urms = the root-mean-squared speed of the
molecules;
m = molecular mass.
urms =
 3RT
M
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urms =
 3RT
M
Sample Exercise 6.14
Calculate the root-mean-square speed of nitrogen molecules
at 300.0 K in meters per second and miles per hour.
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Kinetic theory of gases and …
Boyle’s Law
Charles’ Law
Kinetic theory of gases and …
Avogadro’s Law
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Graham’s Law of Diffusion and Effusion
urms =
 3RT
M
Sample Exercise 6.15
An odorous gas emitted by a hot spring was found to diffuse 2.92 times
slower than helium. What is the molar mass of the emitted gas?
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