Transcript Chapter 9
C H E M I
S T R Y
Chapter 9
Gases: Their Properties and Behavior
STOICHIOMETRIC RELATIONSHIPS WITH GASES
Methanol (CH3OH) can be synthesized by the following
reaction:
CO(g) + 2 H2(g) -- > CH3OH(g)
What volume (in Liters) of hydrogen gas, measured at a
temperature of 355K and a pressure of 738 mmHg, is
required to synthesize 35.7 g of methanol?
EXAMPLES
Determine the mass of NaN3 required for an air
bag to produce 100.0L of N2 gas at 85.0oC and
1.00 atm according to the equation
2 NaN3(s) -- > 2Na(s) + 3N2(g)
PARTIAL PRESSURE AND DALTON’S LAW
Dalton’s Law of Partial Pressures: The total pressure exerted by a
mixture of gases in a container at constant V and T is equal to the
sum of the pressures of each individual gas in the container.
Ptotal = P1 + P2 + … + PN
Moles of component
Mole Fraction (X) =
Total moles in mixture
Xi =
ni
ntotal
or
Xi =
Pi
Ptotal
EXAMPLES
A 1.00 L vessel contains 0.215 moles of N2 gas
and 0.0118 moles of H2 gas at 25.5oC.
Determine moles fraction of each gas
Determine the partial pressure of each gas
Determine the total pressure
EXAMPLES
Determine the number of moles of each gas
present in a mixture of CH4 and C2H6 in a 2.00L
vessel at 25.0oC and 1.50 atm, given that the
partial pressure of CH4 is 0.39 atm
THE KINETIC-MOLECULAR THEORY OF GASES
1.
A gas consists of tiny particles, either atoms or molecules,
moving about at random.
2.
The volume of the particles themselves is negligible compared
with the total volume of the gas; most of the volume of a gas is
empty space.
3.
The gas particles act independently of one another; there are no
attractive or repulsive forces between particles.
4.
Collisions of the gas particles, either with other particles or
with the walls of a container, are elastic (constant temperature).
5.
The average kinetic energy of the gas particles is
proportional to the Kelvin temperature of the sample.
THE KINETIC-MOLECULAR THEORY OF GASES
molar
mass
average
speed
THE KINETIC-MOLECULAR THEORY OF GASES
GRAHAM’S LAW: DIFFUSION AND EFFUSION OF
GASES
Diffusion: The mixing of different gases by molecular motion with
frequent molecular collisions.
GRAHAM’S LAW: DIFFUSION AND EFFUSION OF
GASES
Effusion: The escape of a gas through a pinhole into a vacuum
without molecular collisions.
Graham’s Law:
Rate a
1
m
GRAHAM’S LAW: DIFFUSION AND
EFFUSION OF GASES
In comparing two gases at the same temperature and
pressure
Rate 1
Rate 2
=
√m2
√m1
EXAMPLE
Determine how much faster Helium atoms
moves, on average, than a carbon dioxide
molecule at the same temperature
Determine the molar mass and identity of a gas
that moves 4.67 times as fast as CO2
THE BEHAVIOR OF REAL GASES
The volume of a real gas is larger than predicted
by the ideal gas law.
THE BEHAVIOR OF REAL GASES
Attractive forces between particles become more important
at higher pressures.