KEY
Practice Problems: Gas Laws
CHEM 1A
1. What is the root mean squared velocity of hydrogen gas (H2) at 28.4°C?
28.4ºC
+ 273.15
1 kg
2.016 g/mol
M
301.55 K
3 (8.31451 J/K∙mol) (301.55 K)
3RT
urms N2 =
= 0.002016 kg/mol
103 g
=
= 1931.582935 m/s
(0.002016 kg/mol)
1932 m/s
Answer: ___________________
temperatures, which curve represents the
highest temperature?
b) If each curve represents a different gas at the
same temperature, which curve represents the
gas with the highest molar mass?
C
A
A
# of particles 
2. a) If all curves represent the same gas at different Answers:
B
C
velocity 
3. Which gas effuses faster, NH3 or CCl4? How much faster does it effuse?
lighter gas
Rate effusion NH3
M CCl4
=
Rate effusion CCl4
153.81 g/mol
=
=
17.034 g/mol
M NH3
12.402201597
4.127226672
= 3.004927268
NH3
3.005
CCl4
Answer: __________
effuses __________
times faster than __________
4. Gases X and Y react to form a solid. If the molar mass of gas X is 20.008 g/mol, then what is the
molar mass of gas Y?
Gas X
Gas Y
0 cm
50 cm
100 cm
60.02 cm
MY
Rate diffusion X
Rate diffusion Y
=
MX
45.09 g/mol
Answer: ___________________
MY
60.02 cm / t
39.98 cm / t
=
20.008 g/mol
MY = 45.09309883 g/mol
5. A large balloon filled with helium gas (occupying 293.1 L at 24.8ºC and 769.2 torr) is released.
What volume (in L) would the balloon occupy when it reaches an altitude where the conditions are
–18.7ºC and 383.6 torr?
P1V1
–18.7ºC
+ 273.15
24.8ºC
+ 273.15
297.95 K
=
T1
254.45 K
P2V2
T2
(769.2 torr) (293.1 L)
(383.6 torr) V2
=
(297.95 K)
501.9 L
Answer: ________________
(254.45 K)
V2 = 501.9212246 L
6. A gas in a 975 mL cylinder is at 835 torr. If the gas is compressed by a piston to 225 mL, what is the
pressure of the gas (in atm)?
P1V1 = P2V2
3618.333333 torr
(835 torr) (975 mL) = P2 (225 mL)
P2 = 3618.333333 torr
1 atm
= 4.760964912 atm
760 torr
Note: You could also convert torr to atm before
plugging into Boyle’s Law.
4.76 atm
Answer: ________________
7. Hydrogen gas is collected over water at 27.0ºC and 748.9 torr. If 3.978 L of gas is collected, how
many moles of hydrogen are in the container? (PH2O = 26.5 torr at 27.0ºC)
P total = P H2 + P H2O
P H2 = P total – P H2O
722.4 torr
P H2 = 748.9 torr – 26.5 torr
1 atm
27.0ºC
+ 273.15
= 0.9505263158 atm
760 torr
300.15 K
P H2 = 722.4 torr
PV = nRT
n H2 =
PH2V
RT
(0.9505263158 atm) (3.978 L)
=
(0.08206 L·atm/K·mol) (300.15 K)
= 0.153517915 mol H2
0.1535 mol H2
Answer: ________________
8. If 0.598 mol N2, 0.153 mol O2, and 0.079 mol CO2 are exhaled into a balloon, what volume would
the balloon occupy at STP?
0.598 mol N2
+ 0.153 mol O2
+ 0.079 mol CO2
0.830 mol total
18.6 L
Answer: ________________
@ STP
0.830 mol
22.4 L
1 mol
= 18.592 L
9. 32.42 mol Gas A, 28.15 mol Gas B, and 19.69 mol Gas C are in a 1799 L chamber at STP. What is
the partial pressure of Gas B (in atm)?
PV = nRT
nBRT
PB =
V
(28.15 mol B) (0.08206 L·atm/K·mol) (273.15 K)
=
= 0.3507356839 atm B
(1799 L)
0.3507 atm B
Answer: ________________
10. How many liters of CO2 (at STP) are produced when 250. g of octane (C8H18) are combusted
according to the following equation?
2 C8H18 (l) + 25 O2 (g)  16 CO2 (g) + 18 H2O (g)
250. g
250. g C8H18
1 mol C8H18
16 mol CO2
22.4 L CO2
114.224 g C8H18
2 mol C8H18
1 mol CO2
= 392.2117944 L CO2
392 L CO2
Answer: ________________
11. Ammonia (NH3) is produced industrially at high temperatures and pressures. What is the density of
ammonia gas at 550.°C and 245 atm?
dRT
M =
P
550.ºC
+ 273.15
823.15 K
(17.034 g/mol) (245 atm)
10–3 L
MP
d =
=
= 61.78346087 g/L
= 0.06178346087 g/mL
RT
(0.08206 L·atm/K·mol) (823.15 K)
1 mL
103 g
0.0618 g/mL
Answer: ________________
12. Using the van der Waals equation, calculate the observed pressure of 25.85 moles of xenon gas in a
150.0 L chamber at –25.0°C (a = 4.19 atm·L2/mol2, b = 0.0511 L/mol).
–25.0ºC
n 2
+ 273.15
Pobs + a
V–nb = nRT
V
248.15 K
Pobs
atm·L2
+ 4.19
mol2
25.85 mol Xe
2
150.0 L
1 mol CO2
3.416 atm Xe
Answer: ________________
150.0 L – (25.85 mol Xe) ( 0.0511
L
)
mol
L·atm
= (25.85 mol Xe) ( 0.08206 K·mol ) (248.15 K)
Pobs = 3.415996248 atm