Chapter 12
Gases
What is the pressure of the
gas in the bulb?
1.
2.
3.
4.
5.
Pgas = Ph
Pgas = Patm
Pgas = Ph + Patm
Pgas = Ph - Patm
Pgas = Patm - Ph
What is the pressure of the
gas in the bulb?
1.
2.
3.
4.
5.
Pgas = Ph
Pgas = Patm
Pgas = Ph + Patm
Pgas = Ph - Patm
Pgas = Patm - Ph
If 250 mL of NO is placed in a flask with O2, what
volume of O2 is needed for complete reaction?
2 NO (g)
1.
2.
3.
4.
5.
+ O2 (g)
2 NO2 (g)
100 mL
125 mL
200 mL
250 mL
Cannot be determined from the given information.
If 250 mL of NO is placed in a flask with O2, what
volume of O2 is needed for complete reaction?
2 NO (g)
1.
2.
3.
4.
5.
+ O2 (g)
2 NO2 (g)
100 mL
125 mL
200 mL
250 mL
Cannot be determined from the given information.
If an equal mass of each gas is put into a
separate balloon, which will have the greatest
volume?
1.
2.
3.
4.
5.
Assume that they are all the same temperature
and pressure.
He
H2
N2
Ne
O2
If an equal mass of each gas is put into a
separate balloon, which will have the greatest
volume?
1.
2.
3.
4.
5.
Assume that they are all the same temperature
and pressure.
He
H2
N2
Ne
O2
If equal masses of CH4, C2H6, and C3H8 are placed
in a flask, which of the following is true?
1.
2.
3.
4.
5.
PCH4 = PC2H6 = PC3H8
PCH4 ~ PC2H6 ~ PC3H8
PCH4 > PC2H6 > PC3H8
PCH4 < PC2H6< PC3H8
None of the above
If equal masses of CH4, C2H6, and C3H8 are placed
in a flask, which of the following is true?
1.
2.
3.
4.
5.
PCH4 = PC2H6 = PC3H8
PCH4 ~ PC2H6 ~ PC3H8
PCH4 > PC2H6 > PC3H8
PCH4 < PC2H6< PC3H8
None of the above
Arrange the gases according to increasing
molecular speed.
He (25°C)
1.
2.
3.
4.
5.
He (100°C)
Ne (25°C)
He (25) < He (100) < Ne (25) < Ne (0)
He (25) < He (100) < Ne (0) < Ne (25)
Ne (0) < Ne (25) < He (25) < He (100)
Ne (25) < Ne (0) < He (100) < He (25)
Ne (0) < He (25) < Ne (25) < He (100)
Ne (0°C)
Arrange the gases according to increasing
molecular speed.
He (25°C)
1.
2.
3.
4.
5.
He (100°C)
Ne (25°C)
He (25) < He (100) < Ne (25) < Ne (0)
He (25) < He (100) < Ne (0) < Ne (25)
Ne (0) < Ne (25) < He (25) < He (100)
Ne (25) < Ne (0) < He (100) < He (25)
Ne (0) < He (25) < Ne (25) < He (100)
Ne (0°C)
If a mixture of gas A and gas B is moved from
flask 1 to flask 2, which of the following is true:
1.
2.
3.
4.
5.
PA, PB, and Ptot decrease
flask 1
PA, PB, and Ptot increase
PA and PB decrease, Ptot remains the same
PA, PB, and Ptot remain the same
PA and PB remain the same, Ptot decreases
flask 2
If a mixture of gas A and gas B is moved from
flask 1 to flask 2, which of the following is true:
1.
2.
3.
4.
5.
PA, PB, and Ptot decrease
flask 1
PA, PB, and Ptot increase
PA and PB decrease, Ptot remains the same
PA, PB, and Ptot remain the same
PA and PB remain the same, Ptot decreases
flask 2
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.
2.
3.
4.
40. L
20. L
10. L
5.0 L
Correct Answer:
1.
2.
3.
4.
40. L
20. L
10. L
5.0 L
1
V = constant 
P
PV = constant
Thus,
2.00 atm(10. L) = 0.50 atm (Vfinal)
Vfinal = 2.00 atm(10. L)/0.50 atm =
40. L
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.
2.
3.
4.
1.0 L
2.0 L
0.25 L
4.0 L
Correct Answer:
1.
2.
3.
4.
1.0 L
2.0 L
0.25 L
4.0 L
V = constant  T
V
T
= constant
Thus,
1.0 L/300 K = (Vfinal)/75 K
Vfinal = 75 K/(1.0 L)300 K = 0.25 L
At standard temperature and pressure,
how many moles of gas are present in
a box with a volume of 112 L?
1.
2.
3.
4.
1.00 moles
2.00 moles
5.00 moles
0.200 moles
Correct Answer:
1.
2.
3.
4.
1.00 moles
2.00 moles
5.00 moles
0.200 moles
PV = nRT
V =
nRT
P
=
(1mol)(0.08206 L·atm/mol·K)(273.15K)
1.000 atm
Thus, at STP
22.41 L = 112 L
1.00 mol
n
n = 5.00 moles
= 22.41L
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.
2.
3.
4.
200. g
400. g
800. g
50.0 g
Correct Answer:
1.
2.
3.
4.
200. g
400. g
800. g
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
A gas sample occupies a volume of
4.00 L at 20°C. The temperature at
which the gas would double its
volume is
1.
2.
3.
4.
10°C
40°C
288°C
313°C
Correct Answer:
1.
2.
3.
4.
10°C
40°C
288°C
313°C
V
T
= constant
The temperature scale is absolute,
however;
Vinitial/ (Vfinal) = Tfinal/ (Tinitial)
2 = Tfinal/ 293 K
Tfinal = 586 K, or 313°C
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.
2.
3.
4.
5.
8.0 L
16 L
24 L
32 L
64 L
Correct Answer:
1.
2.
3.
4.
5.
8.0 L
16 L
24 L
32 L
64 L
V  n (constant P, T )
According to Avogadro’s law, mole ratios in
the chemical equation will be volume ratios
under identical conditions. Because the
reactants are in a stoichiometric 3:1 volume
ratio, the product will have stoichiometric
equivalence. Thus,
(16 L N )(2 mol NH /1 mol N ) = 32 L NH
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.
2.
3.
4.
0.17
0.33
0.50
0.67
Pi =
i Ptotal
Correct Answer:
1.
2.
3.
4.
0.17
0.33
0.50
0.67
Pi =
i Ptotal
Xi = Pi/Ptotal
Xi = (300 torr)/(150 + 300 + 450)
torr
Xi = 300 torr/900 torr = 0.33
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
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.
u=
3 RT
M
An unknown gas effuses at half the
rate of helium. This gas is likely to be
which of the following?
1.
2.
3.
4.
5.
H2
CH4
Ne
O2
Ar
Correct Answer:
1.
2.
3.
4.
5.
H2
CH4
Ne
O2
Ar
r1
r2
=
M2
M1
(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
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
Correct Answer:
1. High temperature;
low pressure
2. Low temperature;
high pressure
3. High temperature;
high pressure
4. Low temperature;
pressure and
At lowlow
temperature
high pressure,
intermolecular forces
increase as the molecules
get closer together.