Princeton 2012/Barron 4 th
ed.
Unit 8 – Gases
Multiple Choice (no calculator)
For questions 1-5, one or more of the following responses will apply; each response may be used more than once or not at all in these questions.
(A) H
2
(B) He
(C) O
2
(D) N
2
(E) CO
2
1.
This is the most plentiful gas in the earth’s atmosphere. (P6.1)
2.
A 1 mole sample of this gas occupying 1 liter will have the greatest density. (P6.2)
3.
At a given temperature, this gas will have the greatest rate of effusion.
(P6.3)
4.
The molecules of this nonpolar gas contain polar bonds. (P6.4)
5.
The molecules of this gas contain triple bonds. (P6.5)
6.
The temperature of a sample of an ideal gas confined in a 2.0 L container was raised from 27°C to
77°C. If the initial pressure of the gas was 1,200 mmHg, what was the final pressure of the gas? (P6.6) a.
300 mmHg b.
600 mmHg c.
1,400 mmHg d.
2,400 mmHg e.
3,600 mmHg
7.
A sealed container containing 8.0 grams of oxygen gas and 7.0 of nitrogen gas is kept at a constant temperature and pressure. Which of the following is true? (P6.7) a.
The volume occupied by oxygen is greater than the volume occupied by nitrogen. b.
The volume occupied by oxygen is equal to the volume occupied by nitrogen. c.
The volume occupied by nitrogen is greater than the volume occupied by oxygen. d.
The density of nitrogen is greater than the density of oxygen. e.
The average molecular speeds of the two gases are the same.
8.
A gas sample contains 0.1 mole of oxygen and 0.4 moles of nitrogen. If the sample is at standard temperature and pressure, what is the partial pressure due to nitrogen? (P6.8) a.
0.1 atm b.
0.2 atm c.
0.5 atm d.
0.8 atm e.
1.0 atm

9.
A mixture of gases contains 1.5 moles of oxygen, 3.0 moles of nitrogen, and 0.5 moles of water vapor. If the total pressure is 700 mmHg, what is the partial pressure of the nitrogen gas? (P6.9) a.
70 mmHg b.
210 mmHg c.
280 mmHg d.
350 mmHg e.
420 mmHg
10.
A mixture of helium and neon gases has a total pressure of 1.2 atm. If the mixture contains twice as many moles of helium as neon, what is the partial pressure due to neon? (P6.10) a.
0.2 atm b.
0.3 atm c.
0.4 atm d.
0.8 atm e.
0.9 atm
11.
Nitrogen gas was collected over water at 25°C. If the vapor pressure of water at 25°C is 23 mmHg, and the total pressure in the container is measured at 781 mmHg, what is the partial pressure of the nitrogen gas?
(P6.11) a.
23 mmHg b.
46 mmHg c.
551 mmHg d.
735 mmHg e.
758 mmHg
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12.
When 4.0 moles of oxygen are confined in a 24-liter vessel at
176°C, the pressure is 6.0 atm. If the oxygen is allowed to expand isothermally until it occupies 36 liters, what will be the new pressure?
(P6.12) a.
2 atm b.
3 atm c.
4 atm d.
8 atm e.
9 atm
13.
A gas sample is confined in a 5-liter container. Which of the following will occur if the temperature of the container is increased? (P6.13)
I.
The kinetic energy of the gas will increase.
II.
The pressure of the gas will increase.
III.
The density of the gas will increase. a.
I only b.
II only c.
I and II only d.
I and III only e.
I, II, and III
14.
A 22.0 gram sample of an unknown gas occupies 11.2 liters at standard temperature and pressure. Which of the following could be the identity of the gas? (P6.14) a.
CO
2 b.
SO
3 c.
O
2 d.
N
2 e.
He

15.
A gaseous mixture at constant temperature contains O
2
, CO
2
, and
He. Which of the following lists the three gases in order of increasing average molecular speeds? (P6.15) a.
O
2
, CO
2
, He b.
O
2
, He, CO
2 c.
He, CO
2
, O
2 d.
He, O
2
, CO
2 e.
CO
2
, O
2
, He
16.
Which of the following conditions would be most likely to cause the ideal gas laws to fail? (P6.16)
I.
High pressure
II.
High temperature
III.
Large volume a.
I only b.
II only c.
I and II only d.
I and III only e.
II and III only
17.
Which of the following expressions is equal to the density of helium gas at standard temperature and pressure? (P6.17)
g/L a.
b.
g/L c.
g/L d.
g/L e.
g/L
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18.
An ideal gas is contained in a 5.0 liter chamber at a temperature of
37°C. If the gas exerts a pressure of
2.0 atm on the walls of the chamber, which of the following expressions is equal to the number of moles of the gas? The gas constant, R , is 0.08 (Latm)/(mol-K). (P6.18) a.
moles b.
c.
moles
moles d.
moles e.
moles
19.
Which of the following gases would be expected to have a rate of effusion that is one-third as large as that of
H
2
? (P6.19) a.
O
2 b.
N
2 c.
He d.
H
2
O e.
CO
2

20.
In an experiment H2(g) and O2(g) were completely reacted, above the boiling point of water, according to the following equation in a sealed container of constant volume and temperature:
2H
2
(g) + O
2
(g)

2H
2
O(g)
If the initial pressure in the container before the reaction is denoted as P i
, which of the following expressions gives the final pressure, assuming ideal gas behavior? (P6.20) a.
P i b.
2 P i c.
(3/2) P i
i d.
(2/3) P i e.
(1/2) P i
21.
Nitrogen gas was collected over water at a temperature of 40°C, and the pressure of the sample was measured at 796 mmHg. If the vapor pressure of water at 40°C is 55 mmHg, what is the partial pressure of the nitrogen gas? (P6.21) a.
55 mmHg b.
741 mmHg c.
756 mmHg d.
796 mmHg e.
851 mmHg
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22.
A balloon occupies a volume of 1.0 liter when it contains 0.16 grams of helium at 37°C and 1 atm pressure.
If helium is added to the balloon until it contains 0.80 grams while pressure and temperature are held constant, what will be the new volume of the balloon? (P6.22) a.
0.50 liters b.
1.0 liters c.
2.0 liters d.
4.0 liters e.
5.0 liters
23.
An ideal gas fills a balloon at a temperature of 27°C and 1 atm pressure. By what factor will the volume of the balloon change if the gas in the balloon is heated to 127°C at constant pressure? (P6.23) a.
b.
c.
d.
e.

24.
A gas sample with a mass of 10 grams occupies 6.0 liters and exerts a pressure of 2.0 atm at a temperature of 26°C. Which of the following expressions is equal to the molecular mass of the gas? The gas constant,
R , is 0.08 (L-atm)/(mol-K). (P6.24) a.
b.
c.
d.
e.
25.
Which of the following assumptions is (are) valid based on the kinetic molecular theory? (P6.25)
I.
Gas molecules have negligible volume
II.
Gas molecules exert no attractive forces on one another
III.
The temperature of a gas is directly proportional to its kinetic energy a.
I only b.
III only c.
I and III only d.
II and III only e.
I, II, and III
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26.
A sample of propane, C
3
H
8
, was completely burned in air at STP.
The reaction occurred as shown below.
C
3
H
8
+ O
2
 3 CO
2
+ 4 H
2
O
If 67.2 liters of CO
2
were produced and all of the carbon in the CO
2 came from the propane, what was the mass of the propane sample? (P5.8) a.
11 grams b.
22 grams c.
33 grams d.
44 grams e.
55 grams
27.
Elemental sodium reacts with water to form hydrogen gas as shown below. If a samaple of sodium reacts completely to form 20 liters of hydrogen gas, measured at standard temperature and pressure, what was the mass of the sodium? (P5.15)
2 Na(s) + 2 H
2
O(l)

2 NaOH(aq) +
H
2
(g) a.
5 grams b.
10 grams c.
20 grams d.
30 grams e.
40 grams

28.
What is the STP volume of SO
2
gas produced by the above reaction when
145 grams of ZnSO
3
are consumed?
(P5.16)
ZnSO
3
(s)  ZnO(s) + SO
2
(g) a.
23 liters b.
36 liters c.
45 liters d.
56 liters e.
90 liters
29.
If the reaction above took place at standard temperature and pressure and 150 grams of CaCO
3
(s) were consumed, what was the volume of
CO
2
(g) produced at STP? (P5.19)
CaCO
3
(s) + 2 H
+
(aq)

Ca
+2
(aq) + H
2
O(l) +
CO
2
(g) a.
11 L b.
22 L c.
34 L d.
45 L e.
56 L
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30.
A gaseous mixture at 25°C contained
1 mole of CH
4
and 2 moles of O
2
and the pressure was measured at 2 atm.
The gases then underwent the reaction shown below.
CH
4
(g) + 2 O
2
(g)

CO
2
(g) + 2 H
2
O(g)
What was the pressure in the container after the reaction had gone to completion and the temperature was allowed to return to 25°C?
(P5.20) a.
1 atm b.
2 atm c.
3 atm d.
4 atm e.
5 atm
For questions 31-35, one or more of the following responses will apply; each response may be used more than once or not at all in these questions.
I.
Increased volume
II.
Increased temperature
III.
Increased average kinetic energy
IV.
Increased effusion
V.
Increased pressure
31.
Considering Boyle’s law, the gas will have _______ if the pressure is reduced? (B7.1) a.
I b.
II c.
III d.
IV e.
II and III

32.
There will be _______ if methane,
CH
4
, rather than ethane, CH
3
CH
3
is the gas used under comparable conditions. (B7.2) a.
I and III b.
II c.
III and V d.
IV e.
V
33.
The kinetic molecular theory postulates a direct relationship between (B7.3) a.
I and III b.
II and III c.
III and V d.
IV e.
V
34.
One or more of the changes in this list is inversely related to ALL of the remaining changes assuming all other conditions are kept constant.
(B7.4) a.
I b.
II c.
III d.
IV e.
V
35.
A gas will behave more like an ideal gas if we have an _______ and an
_______. (B7.5) a.
I, II b.
II, III c.
III, V d.
IV, V e.
V, II
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36.
What volume will 2.50 mol of N2 occupy at 45°C and 1.50 atm of pressure? (B7.6) a.
43.5 L b.
6.08 L c.
0.0233 L d.
56.00 L e.
14.9 L
37.
How many moles of helium are needed to fill a balloon that has a volume of 6.45 L and a pressure of
800 mmHg at room temperature of
24°C? Assume ideal gas behavior.
(B7.7) a.
0.288 b.
214 c.
0.278 d.
2.65×10 3 e.
0.255
38.
If ideal gas behavior is assumed, what is the density of neon at STP?
(B7.8) a.
1.11 gL
-1 b.
448 gL
-1 c.
0.009 gL -1 d.
0.901 gL
-1 e.
1.25 gL
-1
39.
A sample of CO has a pressure of 58 mmHg and a volume of 155 mL.
When the CO is quantitatively transferred to a 1.00-L flask, the pressure of the gas will be (B7.9) a.
374 mmHg b.
8990 mmHg c.
111 mmHg d.
8.99 mmHg e.
2.67 mmHg

40.
At 30°C a sample of hydrogen is collected over water [ p
30°C
= 31.82 mmHg] in a 500-mL flask. The total pressure in the collection flask was
745 mmHg. What will be the percent error in the amount of hydrogen reported if the correction for the vapor pressure of water is not made? (B7.10) a.
0.0% b.
+4.5% c.
-4.5% d.
+4.3% e.
-4.3%
41.
What will the total pressure be in a
2.50-L flask at 25°C if it contains
0.016 mol of CO
2
and 0.035 mol of
CH
4
? (B7.11) a.
31.4 mmHg b.
380 mmHg c.
0.041 mmHg d.
935 mmHg e.
1.23 mmHg
42.
The carbon dioxide from the combustion of 1.50 g of C
2
H
6
is collected over water at 25°C. The pressure of CO
2
in the collection flask is 746 mmHg, and the volume is 2.00 L. How much of the CO
2 formed apparently dissolved in the water of the pneumatic trough?
(B7.12) a.
0.0814 mol b.
0.87 g c.
1.79 g d.
0.100 mol e.
2.55 g
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43.
In which of the following is it impossible to predict whether the pressure of a gas will increase, decrease, or stay the same? (B7.13) a.
A gas sample is heated. b.
A gas sample is heated, and the volume is increased. c.
A gas sample is cooled, and some gas is withdrawn. d.
Additional gas is added to a sample of gas. e.
A gas sample is cooled, and the volume is increased.
44.
The kinetic molecular theory predicts that at a given temperature (B7.14) a.
all gas molecules have the same kinetic energy b.
all gas molecules have the same average velocity c.
only real gas molecules collide with each other d.
on the average, heavier molecules move more slowly e.
elastic collisions result in the loss of energy
45.
The effect of increasing the temperature on the pressure may be explained by the kinetic molecular theory as due to (B7.15) a.
the increase in force with which the gas molecules collide with the container walls b.
the increase in rotational energy of the gas molecules c.
the increase in average velocity of the gas molecules, which causes a corresponding increase in the rate of collision with the container walls d.
a decrease in the attractive forces between gas molecules e.
a combination of A and C.

46.
Ideal gases (B7.16) a.
have no volume b.
have no mass c.
have no attractive forces between them d.
have a combination of A and
C e.
have a combination of A and
B
47.
Under which conditions will a real gas behave most like an ideal gas?
(B7.17) a.
high pressure and high temperature b.
low pressure and low temperature c.
low volume and high temperature d.
low pressure and high temperature e.
high pressure and low temperature
48.
Compared to ideal gases, real gases tend to have (B7.18) a.
larger volumes b.
greater kinetic energies c.
lower average kinetic energies d.
lower pressures e.
both A and D
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49.
Under identical conditions gaseous
CO
2
and CCl
4
are allowed to effuse through a pinhole. If the rate of effusion of the CO
2
is 6.3×10
-2
mole s
-1
, what is the rate of effusion of the
CCl
4
? (B7.19) a.
6.3×10
-2
mole s
-1 b.
2.2×10 -1
mole s
-1 c.
1.8×10 -2
mole s
-1 d.
3.4×10 -2
mole s
-1 e.
1.2×10 -1
mole s
-1
50.
A gas has a density, at STP, of 3.48 g
L
-1
. The most reasonable formula for this compound is (B7.20) a.
C
2
H
6 b.
HF c.
CCl
4 d.
C
6
H
6 e.
CaF
2
51.
The number of moles of an ideal gas in a 2.50-L container at 300 K and a pressure of 0.450 atm is ( R = 0.0821
L atm mol
-1
K
-1
) (B7.21) a.
0.0457 b.
21.9 c.
4.93×10 -5 d.
2.03×10 4 e.
6.02
52.
A gas mixture contains twice as many moles of O
2
as N
2
. Addition of 0.200 mol of argon to this mixture increases the pressure from 0.800 atm to 1.10 atm. How many moles of O
2
are in the mixture? (B7.22) a.
0.355 b.
0.178 c.
0.533 d.
0.200 e.
0.0750

53.
A gas in a 1.50-L container has a pressure of 245 mmHg. When the gas is transferred completely to a
350-mL container at the same temperature, the pressure will be
(B7.23) a.
1.05 mmHg b.
1.05 atm c.
2.14 mmHg d.
1050 mmHg e.
9.5×10 -4
atm
54.
At STP a 5.00-L flask filled with air has a mass of 543.251 g. The air in the flask is replaced with another gas, and the mass of the flask is then determined to be 566.107 g. The density of air is 1.290 g L
-1
. What is the gas that replaced the air? (B7.24) a.
Ne b.
O
2 c.
Ar d.
Xe e.
He
55.
What volume of hydrogen gas, at
STP, will a 0.100-g sample of magnesium (molar mass = 24.31) produce when reacted with an excess of HCl? (Mg + 2HCl

MgCl
2
+ H
2
)
(B7.25) a.
92.1 mL b.
46.1 mL c.
184 mL d.
9.2 mL e.
4.6 mL
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56.
In the reaction
CaCO
3
+ 2HCl

H
2
O + CO
2
+ CaCl
2 how many grams of CaCO
3
(molar mass = 100) are needed to produce
3.00 L of CO
2
at STP? (B6.7) a.
13.4 b.
9.11 c.
5.89 d.
300 e.
7.47
57.
How many grams of SO
2
are there in a 4.00-L sample of this compound at
STP? (B6.16) a.
256.2 b.
11.4 c.
358.7 d.
2.78×10 -3 e.
2.86
58.
How many liters of air are needed to completely burn 1 mol of methane in air (20% oxygen) at STP according to the reaction (B6.23)
CH
4
+ 2 O
2

CO
2
+ 2 H
2
O a.
22.4 b.
44.8 c.
11.2 d.
224 e.
64

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Essays
1.
The graph below shows the changes in pressure with changing temperature of gas samples of helium and argon confined in a closed 2-liter vessel. (P6.1)
K, what would be the new pressure of the helium gas?
2.
The reaction below took place, and 1.45 liters of oxygen gas were collected over water at a temperature of 29°C and a pressure of 755 millimeters of mercury. The vapor pressure of water at 29°C is 30.0 millimeters of mercury. (P6.2)
2 KClO
3
(s)

2 KCl + 3 O
2
(g) a.
What is the total pressure of the two gases in the container at a temperature of 200 K?
b.
How many moles of helium are contained in the vessel?
c.
How many molecules of helium are contained in the vessel?
d.
What is the ratio of average speeds of the helium atoms to the averages speeds of the argon atoms?
e.
If the volume of the container were reduced to 1 liter at a constant temperature of 300 a.
What is the partial pressure of the oxygen gas collected?
b.
How many moles of oxygen gas were collected?
c.
What would be the dry volume of the oxygen gas at a pressure of 760 millimeters of mercury and a temperature of 273K?
d.
What was the mass of KClO
3
consumed in the reaction?
3.
Equal molar quantities of two gases, O
2
and H
2
O, are confined in a closed vessel at constant temperature. (P6.3) a.
Which gas, if any, has the greater partial pressure?
b.
Which gas, if any, has the greater density?
c.
Which gas, if any, has the greater average kinetic energy?
d.
Which gas, if any, will show the greater deviation from ideal behavior?
e.
Which gas, if any, has the greater average molecular speed?

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4.
SF
6
, H
2
O, and CO
2
are all greenhouse gases because they absorb infrared radiation in the atmosphere. As such they are of interest to many researchers. (P6.4) a.
Of the three gases, which deviates the most from ideal gas behavior?
b.
If all three ideal gases are held at constant temperature, which gas would have the highest average molecular speed?
c.
A container was with equal amounts H
2
O and CO
2
and the final pressure was measured. Assuming ideal behavior, if SF
6
was then added such that the final pressure was four times that before its addition, the final number of moles of SF6 is how many times that of H
2
O?
d.
If a container held equal molar amounts of all three greenhouse gases, but was then compressed decreasing the volume within, which of the gases has the highest, final partial pressure assuming ideal behavior? e.
Gas molecules exert pressure through collisions with the walls of the containers they are in. If a container is filled with equal amounts of each of the greenhouse gases, which gas undergoes the fewest collisions with the wall of the container per unit time?
5.
A 10.0 gram sample containing calcium carbonate and an inert material was placed in excess hydrochloric acid. A reaction occurred producing calcium chloride, water, and carbon dioxide. (P5.1) a.
Write a balanced equation for the reaction. b.
When the reaction was complete, 900 milliliters of carbon dioxide gas were collected at 740 mmHg and 30°C. How many moles of calcium carbonate were consumed in the reaction? c.
If all of the calcium carbonate initially present in the sample was consumed in the reaction, what percent by mass of the sample was due to calcium carbonate? d.
If the inert material was silicon dioxide, what was the mole ratio of calcium carbonate to silicon dioxide in the original sample?
6.
A gaseous hydrocarbon sample is completely burned in air, producing 1.80 liters of carbon dioxide at standard temperature and pressure and 2.16 grams of water. (P5.2) a.
What is the empirical formula for the hydrocarbon? b.
What was the mass of the hydrocarbon consumed? c.
The hydrocarbon was initially contained in a closed 1.00 liter vessel at a temperature of 32°C and a pressure of 760 millimeters of mercury. What is the molecular formula of the hydrocarbon? d.
Write the balanced equation for the combustion of the hydrocarbon.
7.
Answer the following questions concerning the properties of gases and the theories used to explain their behavior. (B7.1) a.
Describe an ideal gas and compare it to a real gas.

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The kinetic molecular theory is used to explain the behavior of gases. Briefly describe this theory and two of its applications to gases. c.
There are at least two methods for determining molecular masses of gases. What are they? Give the applicable mathematical equations and state what measurements are needed to obtain molar masses. d.
A sample of carbon dioxide in a 2.50-liter flask at 785 torr and 35°C is transferred to a 1.00-liter flask at 405 K. What is the final pressure of the system in atmospheres of pressure?

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Answer Key Unit 8 – Gases
Multiple Choice
1.
D
2.
E
3.
A
4.
E
5.
D
6.
C
7.
B
8.
D
9.
E
10.
C
11.
E
12.
C
13.
C
14.
A
15.
E
16.
A
17.
D
18.
E
19.
D
20.
D
Essays
1.
a. P total
= P
He
+ P
Ar
P
total
= 1 atm + 1.5 atm = 2.5 atm b. PV = nRT
(1 atm)(2.0L) = (n)(.0821)(200K) n = 0.12 moles
21.
B
22.
E
23.
C
24.
A
25.
E
26.
D
27.
E
28.
A
29.
C
30.
B c. d. = = 3.2 to 1 e. P
1
V
1
= P
2
V
2
(1.5 atm)(2.0 L) = P
2
(1.0 L)
P
2
= 3.0 atm
2.
a. P total
= P oxygen
+ P water
755 mmHg = P oxygen
+ 30.0 mmHg
P oxygen
= 725 mmHg b. PV = nRT c. d. n = 0.056 moles
725 mmHg = 0.954 atm
(0.954 atm)(1.45 L) = (n)(0.0821)(302K)
31.
A
32.
D
33.
B
34.
A
35.
A
36.
A
37.
C
38.
D
39.
D
40.
B
41.
B
42.
B
43.
B
44.
D
45.
E
46.
D
47.
D
48.
E
49.
D
50.
D
51.
52.
53.
D
54.
D
55.
56.
57.
58.
A
A
A
A
B
D

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3.
a. Partial pressures depend on number of moles of gas present so since the two gases have the same number of moles, the partial pressures are the same. b. O
2
has the greater density. Density is mass per unit volume. Both gases have the same number of moles in the same volume, but oxygen has heavier molecules so it has a higher density. c. According to the kinetic molecular theory, the average kinetic energy of a gas depends only on the temperature. Both gases are at the same temperature, so they have the same average kinetic energy. d. H
2
O will deviate most from ideal behavior. Ideal behavior for gas molecules assumes that there will be no intermolecular attractions. H
2
O has hydrogen bonding while O
2
does not. H
2
O is polar while O
2
is not. This means that H
2
O has stronger intermolecular attractions which will cause it to deviate more from ideal behavior. e. H
2
O has the greater average molecular speed because according to the equation u rms
= , molecules with the smaller molecular weight will have the greater average molecular speed.
4.
a. H
2
O deviates more drastically from ideal behavior due to very strong hydrogen bonding attractions. A truly ideal gas has no interactions with surrounding molecules.
These hydrogen bonding interactions are why H
2
O is a liquid at room temperature and others are gases. b. As per Graham’s law, the species with the lowest molecular weight would have the greatest average molecular speed. H
2
O is the lightest (mass = 18 g/mol) and hence would be the fastest. c. By Dalton’s law of partial pressures, if SF
6
was added until the pressure was 4 times the pressure with just (an equal mixture of) H
2
O and CO
2
, then there must be 3 times as much SF
6
as H
2
O and CO
2
combined. This means that, in the end, there are 6 times more
SF
6
than H
2
O. For example, imagine starting with 1 atm each of CO
2
and H
2
O. In this case the initial pressure is 2 atm, and to get 8 atm one must add 6 atm of SF
6
which is 6 times that of the H
2
O present. d. All three gases will have identical partial pressures. The equation for partial pressure of any component a is P a
= (P total
)(X a
). Since we know that each has the same mol fraction the total pressure doesn’t matter, and each will have the same partial pressure, relative to one another. e. SF
6
will have the fewest collisions per unit time. Since the kinetic theory assumes that the gas molecules are moving randomly, the one with the most collisions with the walls of the containers will be the one moving the fastest. On the other hand, the slowest

Princeton 2012/Barron 4 th
ed. molecule will have the fewest collisions. The slowest molecule will be the most massive one, as per Graham’s law, which in this case is SF
6
.
5.
a. CaCO
3
+ 2HCl

CaCl
2
+ H
2
O + CO
2 b. PV = nRT 740 mmHg = 0.97 atm
(0.97atm)(0.900L) = (n)(.0821)(303K)
n = 0.035 moles CO
2
0.035 moles CO
2
× c.
Percent by mass = d. Mass of SiO
2
= 10.0g – 3.5g = 6.5 g
= 0.11 g SiO
2
Mole ratio =
6.
a. 2.16 g H
2
O
Every mole of water contains 2 moles of hydrogen so there are 0.240 moles of
hydrogen.
1.80 L CO
2
Every mole of CO
2
contains 1 mole of carbon so there are 0.080 moles of carbon.
There are three times as many moles of H as there are moles of C so empirical formula
is CH
3
. b. H:
C:
Grams hydrocarbon = 0.242 g + 0.961 g = c. PV = nRT
(1.00 atm)(1.00 L) = (n)(.0821)(305K)
n = 0.040 moles
Use mass found in b to find molecular weight of hydrocarbon
MM = grams/mole = 1.203 g/0.040 moles = 30.1 g/mol
CH
3
molar mass = 15
1.203 grams

Princeton 2012/Barron 4 th
ed.
so molecular formula is twice as big as empirical CH
3
= C
2
H
6 d. 2 C
2
H
6
+ 7 O
2

4 CO
2
+ 6 H
2
O
7.
a. An ideal gas is composed of particles in continuous, rapid motion that neither attract nor repel each other. Ideal gas particles occupy no volume. Real gas molecules occupy volume and may attract or repel each other. Cooling a real gas can slow their motions so that attractive forces can cause them to condense. In many cases, especially those that approach low pressure and high temperature, the attractive forces and the relative volumes of real gases are so low that they act very much like ideal gases. b. The kinetic molecular theory states that gases are molecules or atoms in constant random motion and that all collisions are elastic. The volume of gases is negligible compared to the total volume, and attractive forces are also negligible. The average kinetic energy of a gas is directly proportional to the temperature.
This explains Boyle’s law, which states that the pressure and volume of a gas are inversely proportional when temperature is held constant. If the volume of a container is increased, the frequency at which the gas molecules strike the walls decreases because the molecules must travel further to reach each wall. Pressure is proportional to the frequency with which the gas molecules strike the container walls and the average force of each collision. The forces of the collisions do not change because the kinetic energy does not change unless the temperature changes. Therefore the pressure must decrease as the volume increases when temperature is held constant.
The kinetic molecular theory also explains Charles’ law which states that the volume of a gas and the Kelvin temperature are directly proportional when pressure is held constant.
Consider increasing the volume of a gas container. To maintain the pressure, the number and force of collisions with the walls must be kept constant. When the temperature increases, the number of collisions with the walls increases along with the force because of an increase in the average kinetic energy. In total, the pressure remains constant. c. Two methods that give the molar mass use the density of a gas and the ideal gas law equation. The second uses Graham’s Law of effusion. The number of moles, n , in the ideal gas law is calculated as the mass of the sample divided by the molecular mass, M. n=m/molar mass. Substitution into the ideal gas law yields molar mass = mRT/PV. To obtain the molar mass of a gas we need to know its mass and volume (or density), the
Kelvin temperature, and the pressure in atmospheres.
Graham’s law of effusion is
. It requires the measurement of the rate of effusion for a known gas and then measuring the rate of effusion for the gas with an unknown molar mass.

d.
35°C = 308K and 785 torr = 1.033 atm
P
2
= 3.40 atm
Princeton 2012/Barron 4 th
ed.