Chapter 12 Gases

1
Chapter 12Gases
2
What is the pressure of the gas in the bulb?

• Pgas Ph
• Pgas Patm
• Pgas Ph Patm
• Pgas Ph - Patm
• Pgas Patm - Ph

3
What is the pressure of the gas in the bulb?

• Pgas Ph
• Pgas Patm
• Pgas Ph Patm
• Pgas Ph - Patm
• Pgas Patm - Ph

4
If 250 mL of NO is placed in a flask with O2,
what volume of O2 is needed for complete reaction?

• 100 mL
• 125 mL
• 200 mL
• 250 mL
• Cannot be determined from the given information.

5
If 250 mL of NO is placed in a flask with O2,
what volume of O2 is needed for complete reaction?

1. 100 mL
2. 125 mL
3. 200 mL
4. 250 mL
5. Cannot be determined from the given information.

6
If an equal mass of each gas is put into a
separate balloon, which will have the greatest
volume? Assume that they are all the same
temperatureand pressure.

• He
• H2
• N2
• Ne
• O2

7
If an equal mass of each gas is put into a
separate balloon, which will have the greatest
volume? Assume that they are all the same
temperatureand pressure.

• He
• H2
• N2
• Ne
• O2

8
If equal masses of CH4, C2H6, and C3H8 are
placedin a flask, which of the following is
true?

• PCH4 PC2H6 PC3H8
• PCH4 PC2H6 PC3H8
• PCH4 gt PC2H6 gt PC3H8
• PCH4 lt PC2H6lt PC3H8
• None of the above

9
If equal masses of CH4, C2H6, and C3H8 are
placedin a flask, which of the following is
true?

• PCH4 PC2H6 PC3H8
• PCH4 PC2H6 PC3H8
• PCH4 gt PC2H6 gt PC3H8
• PCH4 lt PC2H6lt PC3H8
• None of the above

10
Arrange the gases according to increasing
molecular speed.
He (25C) He (100C) Ne (25C) Ne
(0C)

1. He (25) lt He (100) lt Ne (25) lt Ne (0)
2. He (25) lt He (100) lt Ne (0) lt Ne (25)
3. Ne (0) lt Ne (25) lt He (25) lt He (100)
4. Ne (25) lt Ne (0) lt He (100) lt He (25)
5. Ne (0) lt He (25) lt Ne (25) lt He (100)

11
Arrange the gases according to increasing
molecular speed.
He (25C) He (100C) Ne (25C) Ne
(0C)

1. He (25) lt He (100) lt Ne (25) lt Ne (0)
2. He (25) lt He (100) lt Ne (0) lt Ne (25)
3. Ne (0) lt Ne (25) lt He (25) lt He (100)
4. Ne (25) lt Ne (0) lt He (100) lt He (25)
5. Ne (0) lt He (25) lt Ne (25) lt He (100)

12
If a mixture of gas A and gas B is moved from
flask 1 to flask 2, which of the following is
true

1. PA, PB, and Ptot decrease
2. PA, PB, and Ptot increase
3. PA and PB decrease, Ptot remains the same
4. PA, PB, and Ptot remain the same
5. PA and PB remain the same, Ptot decreases

13
If a mixture of gas A and gas B is moved from
flask 1 to flask 2, which of the following is
true

1. PA, PB, and Ptot decrease
2. PA, PB, and Ptot increase
3. PA and PB decrease, Ptot remains the same
4. PA, PB, and Ptot remain the same
5. PA and PB remain the same, Ptot decreases

14
A gas initially at 2.0 atm is in an adjustable
volume container of 10. L in volume. If the
pressure is decreased to 0.50 atm, what is the
new volume?

1. 40. L
2. 20. L
3. 10. L
4. 5.0 L

15
Correct Answer

1. 40. L
2. 20. L
3. 10. L
4. 5.0 L

1
?

V
constant
P
Thus,
2.00 atm(10. L) 0.50 atm (Vfinal) Vfinal 2.00
atm(10. L)/0.50 atm 40. L
16
Assuming pressure is held constant, to what
volume will a balloon initially at 1.0 L change
if its temperature is decreased from 300 K to 75
K?

1. 1.0 L
2. 2.0 L
3. 0.25 L
4. 4.0 L

17
Correct Answer

1. 1.0 L
2. 2.0 L
3. 0.25 L
4. 4.0 L

?

T
V
constant
Thus,
1.0 L/300 K (Vfinal)/75 K Vfinal 75 K/(1.0
L)300 K 0.25 L
18
At standard temperature and pressure, how many
moles of gas are present in a box with a volume
of 112 L?

1. 1.00 moles
2. 2.00 moles
3. 5.00 moles
4. 0.200 moles

19
Correct Answer

1. 1.00 moles
2. 2.00 moles
3. 5.00 moles
4. 0.200 moles

nRT
PV
(
)
(
)
(
)
K

273.15
K
Latm/mol

0.08206
mol

1
nRT



L

22.41
V
atm

1.000
P
Thus, at STP 22.41 L 112 L 1.00 mol
n n 5.00 moles
20
At standard temperature and pressure, a hot-air
balloon is filled with helium only to a volume of
4480 L. How many grams of helium are needed to
fill the balloon?

1. 200. g
2. 400. g
3. 800. g
4. 50.0 g

21
Correct Answer

1. 200. g
2. 400. g
3. 800. g
4. 50.0 g

At STP 22.41 L 4480 L 1.00 mol n
n 200. moles Since MW(He) is 4.0 g/mol Mass
(200. g)(4.0 g/mol) 800. g
22
A gas sample occupies a volume of 4.00 L at 20C.
The temperature at which the gas would double
its volume is

1. 10C
2. 40C
3. 288C
4. 313C

23
Correct Answer

1. 10C
2. 40C
3. 288C
4. 313C

The temperature scale is absolute,
however Vinitial/ (Vfinal) Tfinal/ (Tinitial)
2 Tfinal/ 293 K Tfinal 586 K, or 313C
24

• N2(g) 3 H2(g) 2 NH3(g)
• At STP, 16 L of N2 and 48 L of H2 are mixed.
  Assuming all the reactants are consumed, how many
  L of NH3 will be produced?

1. 8.0 L
2. 16 L
3. 24 L
4. 32 L
5. 64 L

25
Correct Answer

1. 8.0 L
2. 16 L
3. 24 L
4. 32 L
5. 64 L

?
)
(constant

T
P,
n
V
According to Avogadros law, mole ratios in the
chemical equation will be volume ratios under
identical conditions. Because the reactants are
in a stoichiometric 31 volume ratio, the product
will have stoichiometric equivalence. Thus, (16
L N2)(2 mol NH3/1 mol N2) 32 L NH3
26
A container holds a mixture of oxygen, neon, and
helium gases whose partial pressures are 150
torr, 300 torr, and 450 torr, respectively. The
mole fraction of neon is

1. 0.17
2. 0.33
3. 0.50
4. 0.67

?

P
P
total
i
i
27
Correct Answer

1. 0.17
2. 0.33
3. 0.50
4. 0.67

?

P
P
total
i
i
Xi Pi/Ptotal Xi (300 torr)/(150 300 450)
torr Xi 300 torr/900 torr 0.33
28

• A sample of He gas initially at STP is compressed
  to a smaller volume at constant temperature.
  What effect does this have on the rms speed of
  the atoms?

1. Increases
2. Decreases
3. No effect

29
Correct Answer

1. Increases
2. Decreases
3. No effect

The rms speed is directly proportional to the
square root of the temperature, which does not
change in this example.
30

• An unknown gas effuses at half the rate of
  helium. This gas is likely to be which of the
  following?

1. H2
2. CH4
3. Ne
4. O2
5. Ar

31
Correct Answer

1. H2
2. CH4
3. Ne
4. O2
5. Ar

(r1/2)2 M2/M1 M2 (r1/r2)2M1 M2 (2/1)2(4.0
g/mol) 16.0 g/mol Therefore it could be CH4
32

• Real gases deviate from ideal behavior at
  __________ and _________.

1. High temperature low pressure
2. Low temperature high pressure
3. High temperature high pressure
4. Low temperature low pressure

33
Correct Answer

1. High temperature low pressure
2. Low temperature high pressure
3. High temperature high pressure
4. Low temperature low pressure

At low temperature and high pressure,
intermolecular forces increase as the molecules
get closer together.