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CHEM 111 Chapter 6: Chapter 6Exam


Department
Chemistry
Course Code
CHEM 111
Professor
Prof
Study Guide
Final

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268
CHAPTER 6 | Properties of Gases: The Air We Breathe
6.1. Collect and Organize
In Figure P6.1, the barometer in the middle (b), which is at sea level, has a mercury level intermediate
between a (lower mercury level) and c (higher mercury level).
Analyze
The altitude of Denver, Colorado, is significantly above sea level, and the atmospheric pressure there is
lower than at sea level. The height of the mercury in a barometer depends on the atmospheric pressure:
the higher the pressure, the higher the column of mercury.
Solve
Because Denver has lower atmospheric pressure due to its altitude, the barometer on the left (a)
reflects the pressure in Denver, CO.
Think about It
Altitude above or below sea level isn’t the only factor that changes atmospheric pressure. Weather
(cold fronts, storms, etc.) also change the atmospheric pressure at a given location.
6.2. Collect and Organize
Four illustrations representing molecules in a balloon are shown in Figure P6.2. The spheres represent
helium atoms, and we are asked to choose the drawing that best shows how the helium is distributed in
the balloon.
Analyze
Gases are characterized by having no definite shape or volume. They fill the container they are in and
occupy the container’s entire volume. Also, the atoms or molecules in gases are far apart from each
other.
Solve
Drawing c accurately reflects the distribution of helium atoms in a balloon. The other representations
either show clusters of helium atoms (b and d) or have the helium atoms attached to the wall of the
balloon (a) and therefore the helium gas does not occupy the entire volume.
Think about It
What is not shown in Figure P6.2, but is good to keep in mind, is that gas molecules are in constant
motion.
6.3. Collect and Organize
When the atmospheric pressure outside of the balloon in Figure P6.3 increases, does the balloon (a)
shrink while keeping the molecules randomly distributed in the balloon, (b) expand, or (c) shrink and
condense the molecules of gas into liquid?
Analyze
Boyle’s law states that pressure and volume are inversely proportional to each other.
Solve
If we increase pressure, we decrease volume according to Boyle’s law. This eliminates drawing b. In c,
the molecules of gas are shown to “stick” together and have short distances between them to indicate
that they have condensed. Gases will not condense inside of a balloon simply by changing the outside
pressure. Drawing a is the correct choice because the molecules are still in the gaseous state while the
balloon has shrunk (reduced) in volume.

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Properties of Gases: The Air We Breathe | 269
Think about It
If the atmospheric pressure is lowered then the balloon expands.
6.4. Collect and Organize
When the temperature of the balloon Figure P6.3 increases, does the balloon (a) shrink while keeping
the molecules randomly distributed in the balloon, (b) expand, or (c) shrink and condense the
molecules of gas into liquid?
Analyze
Charles’s law states that volume and temperature of a gas are directly proportional.
Solve
If we increase the temperature, Charles’s law states that the volume of the balloon increases. This is
represented by diagram b.
Think about It
If the temperature is increased too much, the balloon will burst.
6.5. Collect and Organize
When the amount of gas is increased in a balloon and temperature and pressure remain constant
(Figure P6.5), does the volume of the balloon (a) stay the same, (b) decrease, or (c) increase?
Analyze
Avogadro’s law states that volume and the number of moles of gas are directly proportional.
Solve
As we increase the amount of gas in a balloon, we increase the moles of gas in the balloon. Applying
Avogadro’s law, drawing c represents the addition of gas to the balloon.
Think about It
If the container is rigid (not expandable like a balloon), then adding more gas would increase the
pressure, but not the volume.
6.6. Collect and Organize
The plot in Figure P6.6 shows the volume (V) as a function of the inverse of pressure (1/P). Line 2 in
the plot diverges from line 1 at the origin and is above line 1. We are asked which line represents the
higher temperature.
Analyze
Because V is inversely proportional to P, the plot of V versus 1/P will give a straight line for a sample
of gas. According to Charles’s law, a gas sample held at constant pressure at higher temperatures has a
larger volume.
Solve
A gas sample at a higher temperature has a larger volume at a given 1/P value than one at a lower
temperature. Therefore, line 2 represents the gas sample at higher temperature.
Think about It
The lines converge at the origin because at infinite pressure the volume of gas will be zero.
6.7. Collect and Organize
The plot in Figure P6.7 shows the volume (V) as a function of temperature (T). Line 2 is higher on the
(V) axis than line 1. We are asked which line represents the higher pressure and whether an absolute
temperature scale is shown.

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270 | Chapter 6
Analyze
According to Charles’s law, volume and temperature are directly proportional. The higher the
temperature of the gas sample, the higher the volume. Pressure and volume, on the other hand, are
inversely proportional according to Boyle’s law. The higher the pressure, the lower the volume.
Solve
Since line 1 is always below line 2 on the plot (volume at any given temperature is smaller for the gas
sample in line 1), line 1 represents the gas at a higher pressure. The x-axis is not on the absolute
temperature scale. If it were, line 1 and line 2 would meet at T = 0 K.
Think about It
A plot of pressure versus temperature would also show that at 0 K the pressure is also zero.
6.8. Collect and Organize
The plot in Figure P6.8 shows two lines for the relationship between volume and pressure. We are
asked which line is not consistent with the ideal gas law.
Analyze
By Boyle’s law, volume and pressure are inversely proportional. This means that as pressure (P)
increases, the volume (V) of the gas decreases. This relationship is also evident in the ideal gas law
PV = nRT
if we rearrange the equation to
or
nRT c
PP
VV
where c = constant.
Solve
Line 1 in Figure P6.8 is the line that is inconsistent with the ideal gas law because it shows that as
pressure increases, the volume increases. Line 2 is consistent with the ideal gas law because it shows
the inverse proportionality between P and V.
Think about It
The linear line would be correct if either V or P were plotted on the y-axis and T were plotted on the x-
axis, keeping the quantity not plotted a constant.
6.9. Collect and Organize
The plot of volume versus temperature in Figure P6.9 contains two lines: one with a positive slope as
temperature increases, the other with a negative slope as the temperature increases. Which line is
inconsistent with the ideal gas law?
Analyze
The ideal gas law shows the direct proportionality between V and T as
or
PV nRT
nRT
VVcT
P
where c = nR/P.
Solve
By the ideal gas law, as temperature increases volume also increases. This is shown by line 1 in Figure
P6.9. Line 2, therefore, is inconsistent with the ideal gas law.
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