Chapter 10 Gases

1
Chapter 10Gases
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?

• 40. L
• 20. L
• 10. L
• 5.0 L

3
Correct Answer

• 40. L
• 20. L
• 10. L
• 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
4
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?

• 1.0 L
• 2.0 L
• 0.25 L
• 4.0 L

5
Correct Answer

• 1.0 L
• 2.0 L
• 0.25 L
• 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
6
At standard temperature and pressure, how many
moles of gas are present in a box with a volume
of 112 L?

• 1.00 moles
• 2.00 moles
• 5.00 moles
• 0.200 moles

7
Correct Answer

• 1.00 moles
• 2.00 moles
• 5.00 moles
• 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
8
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?

• 200. g
• 400. g
• 800. g
• 50.0 g

9
Correct Answer

• 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
10
A gas sample occupies a volume of 4.00 L at 20C.
The temperature at which the gas would double
its volume is

• 10C
• 40C
• 288C
• 313C

11
Correct Answer

• 10C
• 40C
• 288C
• 313C

The temperature scale is absolute,
however Vinitial/ (Vfinal) Tfinal/ (Tinitial)
2 Tfinal/ 293 K Tfinal 586 K, or 313C
12

• 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?

• 8.0 L
• 16 L
• 24 L
• 32 L
• 64 L

13
Correct Answer

• 8.0 L
• 16 L
• 24 L
• 32 L
• 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
14
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

• 0.17
• 0.33
• 0.50
• 0.67

?

P
P
total
i
i
15
Correct Answer

• 0.17
• 0.33
• 0.50
• 0.67

?

P
P
total
i
i
Xi Pi/Ptotal Xi (300 torr)/(150 300 450)
torr Xi 300 torr/900 torr 0.33
16

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

• H2
• CH4
• Ne
• O2
• Ar

17
Correct Answer

• H2
• CH4
• Ne
• O2
• 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
18

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

• High temperature low pressure
• Low temperature high pressure
• High temperature high pressure
• Low temperature low pressure

19
Correct Answer

• High temperature low pressure
• Low temperature high pressure
• High temperature high pressure
• Low temperature low pressure

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