Gases ❮ 117- C—This question relates to the combined gas
law:PV
T
11
1=
PV
T
22
2. Since the pressure remains
constant, the pressures may be removed from
the combined gas law to produce Charles’s law:
V
T
(^1)
1
=
V
T
(^2)
2
. This equation may be rearranged to
T 2 =TV
V
12
1. The doubling of the volume means
V 2 = 2 V 1. On substituting, T 2 =
TV
V
11 2
1, giving
T 2 = 2 T 1. The identity of the gas is irrelevant in
this problem.- C—This problem depends on the ideal gas equa-
tion: PV = nRT. R, V, and T are known, and by
using the partial pressure for a gas, the number
of moles (n) of that gas may be determined. To
convert from moles to mass, the molar mass of
the gas is necessary. - B—Since T and P are known, and since the moles
(n) can be determined from the masses given,
this question could use the ideal gas equation.
The number of moles of each gas is 0.50. Equal
moles of gases, at the same T and P, have equal
volumes, which eliminates answer choice D.
Equal volume also means that the greater mass
has the greater density, eliminating choice A.
The average kinetic energy of a gas depends
on the temperature. If the temperatures are
the same, then the average kinetic energy is the
same, eliminating C. Finally, at the same tem-
perature, heavier gases travel slower than lighter
gases. Nitrogen is lighter than argon, so it travels
at a faster average speed, making B the correct
answer. You may find this type of reasoning
process beneficial on any question in which you
do not immediately know the answer.- A—This experiment requires the ideal gas equa-
tion. The mass of the solid is needed (to convert
to moles); this eliminates answer choice D. The
volume, temperature, and pressure must also be
measured during the experiment, eliminating
choices B and C. The measured pressure is the
total pressure. Eventually the total pressure must
be converted to the partial pressure of the gas
using Dalton’s law. The total pressure is the sum
of the pressure of the gas plus the vapor pressure
of water. The vapor pressure of water can be
looked up in a table when the calculations are
performed (only the temperature is needed to
❯ Answers and Explanations
- Three identical steel containers at the same
temperature are filled with gas samples. One
container has 16 g of methane, CH 4 ; another
has 44.0 g of carbon dioxide, CO 2 ; and the third
has 146 g of sulfur hexafluoride, SF 6. Pick the
FALSE statement from the following list:
(A) The densities decrease in the following
order: sulfur hexafluoride > carbon dioxide
methane.
(B) Each container has the same number of
molecules.
(C) The pressure in each container is the same.
(D) The molecules in each container have the
same average speed.
- Which of the following places the gases in order
of increasing deviation from ideal behavior?
(A) He < SO 2 < CH 4 < O 2
(B) He < O 2 < CH 4 < SO 2
(C) He < CH 4 < O 2 < SO 2
(D) CH 4 < O 2 < He < SO 2
19. Each of four 10.0 L containers is filled with a
different noble gas (He, Ne, Ar, and Kr). Each
container contains 0.5 mole of gas at 298 K.
Assuming all four gases are behaving ideally,
which of the following is the same for all four
samples?
(A) average speed of the atoms
(B) density of the gas in the container
(C) All properties are the same for gases behaving
ideally.
(D) average kinetic energy of the atoms
20. Each of four 5.0 L containers is filled with a
different gas (He, CH 4 , O 2 , and CO 2 ). Each
container contains 0.75 mole of gas at 273 K. If
one of the containers springs a small leak, which
of the following will change in that container?
(A) moles, temperature, and pressure
(B) moles and pressure
(C) temperature and pressure
(D) moles and temperature