Chapter Five:
GASES
p178
2
Contentsp178
3
5-1 Pressurep179
Why study gases?
1. An understanding of real world phenomena.
2. An understanding of how science “works.”
4
A Gas
• Uniformly fills any container.
• Mixes completely with any other gas.
• Exerts pressure on its surroundings.
5
Pressure
• SI units = Newton/meter2 = 1 Pascal (Pa)
• 1 standard atmosphere = 101,325 Pa
• 1 standard atmosphere = 1 atm =
760 mm Hg = 760 torr
Units of Pressure
…is equal to force/unit areap180
6
Ex 5.1 Pressure Conversions
The pressure of a gas is measured as 49 torr. Represent
this pressure in both atmospheres and pascals.
P181
Solution:
7
5-2 The Gas Laws of Boyle, Charles, andAvogadro
p181
Boyle’s Law
8
p182
9
p183
Ex 5.2 Boyle’s LawSulfur dioxide (SO2), a gas that plays a central role in the
formation of acid rain, is found in the exhaust of automobiles
and power plants. Consider a 1.53-L sample of gaseous SO2
at a pressure of 5.6 × 103 Pa. If the pressure is changed to 1.5
× 104 Pa at a constant temperature, what will be the new
volume of the gas?
P183
Solution:
11
p184
12
p184
13
Liquid Nitrogen and a Balloon
14
Volume and Temperature
What law results from observations
like these?
The volume of a gas depends on the
temperature of the gas (constant P and n).
15
Charles’s Lawp184
Absolute zero
Volume and temperature are directly related
(constant P and n).
16
Charles’s Law
17
p184
18
Other Laws
Pressure and Volume are inversely related
(constant T and n)
Boyle’s Law
PV = k
19
Boyle’s Law
20
Ex 5.4 Charles’s Law
A sample of gas at 15℃ and 1 atm has a volume of 2.58
L. What volume will this gas occupy at 38℃ and 1 atm?
P185
Solution:
Ex 5.5 Avogadro’s Law
Suppose we have a 12.2-L sample containing 0.5 mol
oxygen gas (O2) at a pressure of 1 atm and a
temperature of 25℃. If all this O2 were converted to
ozone (O3) at the same temperature and pressure and
pressure, what would be the volume of the ozone?
P186
Solution:
22
Gas Volume, Pressure, and Concentration
23
5-3 The Ideal Gas Lawp186
24
Ideal Gas Law
We can bring all of these laws together into one
comprehensive law:
V = bT
PV = k
V = an
PV = nRT
25
Ex 5.6 Ideal Gas Law
A sample of hydrogen gas (H2) has a volume of 8.56 L at
a temperature of 0℃ and a pressure of 1.5 atm. Calculate
the moles of H2 molecules present in this gas sample.
P187
Solution:
26
5-4 Gas Stoichiometryp190
27
A sample of nitrogen gas has a volume of 1.75 L at STP.
How many moles of N2 are present?
P191Ex 5.11 Gas Stoichiometry
Solution:
28
Ex 5.14 Gas Denisty/Molar Mass
The density of a gas was measured at 1.50 atm
and 27℃ and found to be 1.95 g/L. Calculate the
molar mass of the gas.
P193
Solution:
5-5 Dalton’s Law of Partial Pressuresp194
For a mixture of gases in a container,
PTotal = P1 + P2 + P3 + . . .
30
Mole fraction
p195
Ex 5.15 Dalton’s LawP195
Mixtures of helium and oxygen can be used in scuba divingtanks to help prevent “the bends.”For a particular dive, 46L He at 25℃ and 1.0 atm and 12 L O2 at 25℃ and 1.0 atmwere pumped into a tank with a volume of 5.0 L. Calculatethe partial pressure of each gas and the total pressure in thetank at 25℃.Solution:
P198Ex 5.18 Gas Collection over WaterA sample of solid potassium chlorate (KClO3) was
heated in a test tube (see Fig. 5.13) and decomposed by
the following reaction:
The oxygen produced was collected by displacement of
water at 22℃ at a total pressure of 754 torr. Calculate the
partial pressure of O2 in the gas collected and mass of
KClO3 in the sample that was decomposed.
)(3O)(2KCl)(KClO2 23 gss
Solution:
34
5-6 The Kinetic Molecular Theory ofGases
p199
So far we have considered “what happens,”but
not “why.”
In science, “what”always comes before “why.”
35
Kinetic Molecular Theory
Assumptions:
1. Gas particles are in rapid motion, colliding
with container walls.
36
Kinetic Molecular Theory
Assumptions:
2. Gas particles have negligible size
compared to the distances between them.
37
Kinetic Molecular Theory
Assumptions:
3. Gas particles have no attraction for one
another.
38
Kinetic Molecular Theory
Assumptions:
4. Absolute temperature of the gas is a
measure of the average kinetic energy of
the gas particles.
39
Kinetic Molecular Theory
40
Kinetic Molecular Theory
Animation: Visualizing Molecular Motion (many
molecules)
41
Kinetic Molecular Theory
Animation: Kinetic Molecular Theory/Heat-
Transfer
42
Molecular View of Boyle’s Law
43
Molecular View of Charles’s Law
44
Molecular View of The Ideal Gas Law
45
Video: Collapsing Can
46
p200
Kinetic molecular theory(KMT)
47
Pressure and Volume (Boyle’s Law)
p200
Pressure and Temperature
Volume and Temperature (Charles’s Law)
48
Volume and Number of Moles (Avogadrao’s Law)
Mixture of gases (Dalton’s Law)
p202
Deriving the Ideal Gas Law p203
The Meaning of Temperature p204
Root Mean Square Velocity
Ex 5.19 Root Mean Square Velocity P205
Calculate the root mean square velocity for the atoms
in a sample of helium gas at 25℃.Solution:
=
52
5-7 Effusion and Diffusionp206
Diffusion is the term used to describe themixing of gases.
The rate of effusion measuresthe speed at which the gas istransferred into the chamber.
Figure 5-22
Effusion
P206Ex 5.20 Effusion RatesCalculate the ratio of the effusion rates of hydrogen gas (H2)
and uranium hexafluoride (UF6), a gas used in the enrichment
process to fuel for nuclear reactors (see Fig. 5.23).
Figure 5.23Solution:
54
Effusion
55
Diffusion
56
Ammonia and HCl
NH3(g) + HCl(g) → NH4Cl(s) White solidp207
Figure 5-24
58
We must correct for ideal gas behavior when
the pressure of the gas is high.
smaller volume
the temperature is low.
attractive forces become important
5-8 Real Gases p208
59
Plots of PV/nRT Versus Pfor Several Gases (200 K)
Figure 5.25
p208
60
Plots of PV/nRT Versus P forNitrogen Gas at Three Temperatures
Figure 5.26
p208
Real Gases
[ ]P a V nb nRTobs2( / ) n V
p208
corrected pressure
Pideal
corrected volume
Videal
62
5-9 Characteristics of Several Real Gasesp211
A low value for a reflects weak intermolecular
forces among the gas molecules.
Based on the this behavior we can surmise that
the importance of intermolecular increases in
this order.
63
p2115-10 Chemistry in the Atmosphere
64
Table 5.4 Atmospheric Composition Near SeaLevel (Dry Air)
p211
p211
Figure 5.31
Concentration for Some SmogComponents vs. Time of Day
A Schematic Diagram of a Scrubber
Figure 5.33
p214
67
Photochemical smog p213