GAS LAWS PACKET - HONORS ONLY UNIT 6
DALTON’s LAW OF PARTIAL PRESSURE
Dalton’s law says that the sum of the individual pressures of all the gases that make
up a mixture is equal to the total pressure or : PT = P1 + P2 + P3 +…The partial pressure
of each gas is equal to the mole fraction of each gas x total pressure.
PT = P1 + P2 + P3 +…
or
moles gasx
total moles
x
PT = PX
1) A 250 ml sample of oxygen is collected over water at 25 C and 760 mm Hg pressure.
What is the pressure of the dry gas alone? (V.P. of water at 25 C = 23.8 mm Hg)
736mm Hg
2) A 32.0 ml sample of hydrogen is collected over water at 20 C and 750 mm Hg
pressure. What is the volume of the dry gas at STP? ( V.P. of water at 20 C = 17.5
mm Hg)
28.7ml
3) A 54.0 ml sample of oxygen is collected over water at 23 C and 770.0 mm Hg pressure.
What is the volume of the dry gas at STP? ( V.P. of water at 23 C = 21.1 mm Hg)
49ml
4) A mixture of 2.00 moles of H2, 3.00 moles of NH3, 4.00 moles of CO2, and 5.00 moles of N2
exerts a total pressure of 800 mm Hg. What is the partial pressure of each gas?
114.3mg, 171.4mm Hg, 228.6mm Hg, 285.7mm Hg
5) The partial pressure of F2 in a mixture of gases where the total pressure is 1.00 atm is
300 mm Hg. What is the mole fraction of F2?
.39 atm
6) 6 g NH3, 100 g SO3 and 5L of O2 are put in a container at STP. If the total
pressure is 2500 mm Hg, calculate the partial pressure of each gas.
481 mm Hg, 1717mm Hg, 302 mm Hg
7) 200 mL of H2 gas are collected in a bottle over water at 25C. If the total pressure
inside the bottle is 950 mm Hg, calculate the pressure of the pure dry hydrogen. (V.P.
of water at 25 C = 23.8 mm Hg)
926mm Hg
8) 24.0 grams of NH3, 21.0 grams of CO2 and 34.0 grams of N2 exert a total
pressure of 642 mm Hg. Find the partial pressure of each component.
292 mm Hg, 99.4 mm Hg, 251 mm Hg
9) A 4.60 liter cylinder contains 1.6 moles of helium, 0.34 mole of neon, and 1.2 moles of
argon at 27C. Find the partial pressure of neon in atm.
1.8 atm
IDEAL GAS LAW
P = pressure in atmospheres
PV
=
nRT
V = volume in liters
n = number of moles of gas
R = Universal Gas Constant 0.0821 L • atm/mole • K
1) A 9.81 liter cylinder contains 23.5 moles of nitrogen at 23C. What pressure
is exerted by the gas? Answer in atmospheres.
58.2 atm
2) A pressure of 850 mm Hg is exerted by 28.6 grams of sulfur dioxide at a
temperature of 40C. Calculate the volume of the vessel holding the gas.
10.3 L
3) How many moles of NO2 are in a 5.24 liter cylinder if the pressure is 1.62
atmospheres at 17C?
.357 moles
4) At what Celsius temperature will argon have a density of 10.3 grams/liter and a
pressure of 6.43 atmospheres?
31.2 C
5) Calculate the mass of ammonia in a 6.64 liter cylinder if the pressure is 4.76
atmospheres at a temperature of 25C?
22.0g
6) Calculate the pressure exerted by 0.25 moles of O2 gas in a 2 liter cylinder at
30C.
3.1 atm
7) What is the density of neon at 40C and 1.23 atmospheres?
.958 g/L
8) The density of an unknown gas at 20C and 749 mm Hg is 1.31 grams/liter.
Estimate the molar weight of the gas.
31.9g
9) Calculate the temperature of 3 moles of H2 gas if it is pumped into a 5 liter
cylinder at a pressure of 4 atmospheres.
81.2 K
10) What volume would 0.3 moles of N2 gas occupy at 100C and 0.5 atm of
pressure?
18.4 L
11) How many moles of SO2 are contained in a 4 liter cylinder at 300 K and a
pressure of 1520 mm Hg?
.325 moles
12) The contents of a 1.85 liter gas cylinder exerts a pressure of 3.68 atm
(atmospheres) at 24C. How many moles of gas are in the cylinder?
.289 moles
13) Calculate the pressure of 8 g O2 (g) in a 4 liter flask at 30C.
1.55 atm
14) If a 2.5 g sample of a gas in a 300 mL flask has a pressure of 1500 mm Hg at
20C, calculate the molecular weight of this gas.
101.8g/mole
15) What volume will 20 moles of CO2 occupy at 25C and 600 mm Hg?
620 L
16) If 5.0 x 1024 molecules of CO2 gas are at STP, what volume would they
occupy?
186L
17) Find the pressure in mm Hg produced by 2.35 grams of carbon dioxide in a 5.00 liter
vessel at 18C.
193.8mm Hg
18) At what temperature will 0.750 mole of chlorine in a 15.7 liter vessel exert a pressure
of 756 mm Hg?
252K
19) How many grams of carbon monoxide must be placed into a 40.0 liter tank to develop a
pressure of 965 mm Hg at 23C?
58.5g
20) If 0.710 grams of an unidentified gas is placed in a 390 ml cylinder, at 52C the gas
yields a pressure of 520 mm Hg. Find the molar weight of the gas.
71.4g/mole
GRAHAM’S LAW OF EFFUSION/DIFFUSION
Graham’s Law says that a gas will effuse at a rate that is inversely proportional to
the square root of its molecular mass (MM).
Rate1
Rate2
=
√
MM2
MM1
1) Under the same conditions of temp and pressure, how many times faster will hydrogen
effuse compared to carbon dioxide?
4.69x faster
2) What is the relative rate of diffusion of NH3 compared to He? Does NH3 effuse
faster or slower than He?
.485
3) If the He in the above problem takes 20 seconds to effuse, how long will NH 3 take?
41 sec
4) An unknown gas diffuses 0.25 times as fast as He. What is the molecular mass of the
unknown gas?
64g/mole
5) Compare the rates of diffusion of oxygen O2 to SO3 gas at 25C.
1.58x
6) Find the ratio of the effusion rate of CH4 to that of C2H6.
1.37x
7) If CO2 diffuses from a flask in 30 seconds and an unknown gas diffuses from the
same flask in 5 minutes, calculate the molecular weight of this unknown gas.
4400g/mole
8) 62 seconds are required for the escape of a specified number of moles of nitrogen
from an effusion apparatus. If the escape of the same number of moles of an unknown
gas requires 51 seconds, find the molar weight of the unknown.
19.44g/mole
9) 45 seconds are required for a given number of moles of hydrogen to effuse through a
small opening. How long will it take for the same number of moles of oxygen to escape
if the starting conditions are the same?
180 sec
MULTIPLE CHOICE
1. Hydrogen and oxygen gases are in a container where a total pressure of 4 kPa is
exerted. If the hydrogen gas is exerting a pressure of 3kPa, the oxygen must be
exerting a pressure of ____ kPa.
a. 1
b. 2
c. 3
d. 4
2. Dalton’s law of
pressure states the relationship between the total
pressure in a container and the sum of the pressures of the gases in that container.
a. unit
b. total
c. partial
d. average
3. Grahams’ law, states the relationship between the
rate of diffusion of the gas at a constant temperature.
a. volume
c. number of molecules
b. pressure
d. molecular mass
of a gas and the
4. If a molecule of gas A has 4 times the mass of a molecule of gas B, gas A will
diffuse
as fast as gas B at constant temperature.
a. ½
b. ¼
c. 2 times
d. 4 times
Honor Unit 6: Gas Laws
Multiple Choice
Identify the choice that best completes the statement or answers the question.
1. ANS: E
2.
ANS: B
3.
ANS: C
4.
ANS: A
5. ANS: A
6.
ANS: D
7.
ANS: B
8.
ANS: E
9. ANS: C
10.
ANS: C
11.
ANS: D
12.
ANS: A
13. ANS: D
14.
ANS: C
15.
ANS: D
16.
ANS: C
17. ANS: E
18.
ANS: B
19.
ANS: C
20.
ANS: E
21. ANS: C
22.
ANS: B
23.
ANS: A
24.
ANS: A
25. ANS: A
____
1. A sample of gas (24.2 g) initially at 4.00 atm was compressed from 8.00 L to 2.00 L at constant temperature.
After the compression, the gas pressure was __________ atm.
a. 4.00
b. 2.00
c. 1.00
d. 8.00
e. 16.0
____
2. A balloon originally had a volume of 4.39 L at 44 °C and a pressure of 729 torr. The balloon must be cooled
to __________°C to reduce its volume to 3.78 L (at constant pressure).
a. 38
b. 0
c. 72.9
d. 273
e. 546
____
3. A sample of He gas (2.35 mol) occupies 57.9 L at 300.0 K and 1.00 atm. The volume of this sample is
__________ L at 423 K and 1.00 atm.
a. 0.709
b. 41.1
c. 81.6
d. 1.41
e. 57.9
____
4. The reaction of 50 mL of Cl2 gas with 50 mL of CH4 gas via the equation:
will produce a total of __________ mL of products if pressure and temperature are kept constant.
a. 100
b. 50
c. 200
d. 150
e. 250
____
5. The amount of gas that occupies 60.82 L at 31°C and 367 mm Hg is __________ mol.
a. 1.18
b. 0.850
c. 894
d. 11.6
e. 0.120
____
6. The volume of 0.65 mol of an ideal gas at 365 torr and 97°C is __________ L.
a. 0.054
b. 9.5
c. 11
d. 41
e. 2.4  10-2
____
7. The density of ammonia gas in a 4.32 L container at 837 torr and 45.0°C is __________ g/L.
a. 3.86
b. 0.719
c. 0.432
d. 0.194
e. 4.22  10-2
____
8. The density of N2O at 1.53 atm and 45.2°C is __________ g/L.
a. 18.2
b. 1.76
c. 0.388
d. 9.99
e. 2.58
____
9. The molecular weight of a gas is __________ g/mol if 3.5 g of the gas occupies 2.1 L at STP.
a. 41
b. 5.5  103
c. 37
d. 4.6  102
e. 2.7  10-2
____ 10. The Mond process produces pure nickel metal via the thermal decomposition of nickel tetracarbonyl:
Ni(CO)4 (l)  Ni (s) + 4CO (g).
What volume (L) of CO is formed from the complete decomposition of 444 g of Ni(CO)4 at 752 torr and
22.0°C?
a. 0.356
b. 63.7
c. 255
d. 20.2
e. 11.0
____ 11. A vessel contained N2, Ar, He, and Ne. The total pressure in the vessel was 987 torr. The partial pressures of
nitrogen, argon, and helium were 44.0, 486, and 218 torr, respectively. The partial pressure of neon in the
vessel was __________ torr.
a.
b.
c.
d.
e.
42.4
521
19.4
239
760
____ 12. The pressure in a 12.2 L vessel that contains 2.34 g of carbon dioxide, 1.73 g of sulfur dioxide, and 3.33 g of
argon, all at 42°C is __________ mm Hg.
a. 263
b. 134
c. 395
d. 116
e. 0.347
____ 13. In a gas mixture of He, Ne, and Ar with a total pressure of 8.40 atm, the mole fraction of Ar is __________ if
the partial pressures of He and Ne are 1.50 and 2.00 atm, respectively.
a. 0.179
b. 0.238
c. 0.357
d. 0.583
e. 0.417
____ 14. A mixture of He and Ne at a total pressure of 0.95 atm is found to contain 0.32 mol of He and 0.56 mol of Ne.
The partial pressure of Ne is __________ atm.
a. 1.7
b. 1.5
c. 0.60
d. 0.35
e. 1.0
____ 15. A sample of N2 gas (2.0 mmol) effused through a pinhole in 5.5 s. It will take __________ s for the same
amount of CH4 to effuse under the same conditions.
a. 7.3
b. 5.5
c. 3.1
d. 4.2
e. 9.6
____ 16. A sample of He gas (2.0 mmol) effused through a pinhole in 53 s. The same amount of an unknown gas,
under the same conditions, effused through the pinhole in 248 s. The molecular mass of the unknown gas is
__________ g/mol.
a. 0.19
b. 5.5
c. 88
d. 19
e. 350
____ 17. Which of the following statements about gases is false?
a. Gases are highly compressible.
b. Distances between molecules of gas are very large compared to bond distances within
molecules.
c. Non-reacting gas mixtures are homogeneous.
d. Gases expand spontaneously to fill the container they are placed in.
e. All gases are colorless and odorless at room temperature.
____ 18. One significant difference between gases and liquids is that __________.
a. a gas is made up of molecules
b. a gas assumes the volume of its container
c. a gas may consist of both elements and compounds
d. gases are always mixtures
e. All of the above answers are correct.
____ 19. Molecular compounds of low molecular weight tend to be gases at room temperature. Which of the following
is most likely not a gas at room temperature?
a. Cl2
b. HCl
c. LiCl
d. H2
e. CH4
____ 20. The volume of an ideal gas is zero at __________.
a. 0°C
b. -45°F
c. -273 K
d. -363 K
e. -273°C
____ 21. A mixture of Xe, Kr, and Ar has a total pressure of 6.70 atm. What is the mole fraction of Kr if the partial
pressures of Xe and Ar are 1.60 atm and 2.80 atm, respectively.
a. 0.174
b. 0.256
c. 0.343
d. 0.481
e. 0.570
____ 22. Of the following gases, __________ will have the greatest rate of effusion at a given temperature.
a. NH3
b. CH4
c. Ar
d. HBr
e. HCl
____ 23. Arrange the following gases in order of increasing average molecular speed at 25°C.
Cl2, O2, F2, N2
a.
b.
c.
d.
e.
Cl2 < F2 < O2 < N2
Cl2 < O2 < F2 < N2
N2 < F2 < Cl2 < O2
Cl2 < F2 < N2 < O2
F2 < O2 < N2 < Cl2
____ 24. An ideal gas differs from a real gas in that the molecules of an ideal gas __________.
a. have no attraction for one another
b. have appreciable molecular volumes
c. have a molecular weight of zero
d. have no kinetic energy
e. have an average molecular mass
____ 25. Which one of the following gases would deviate the least from ideal gas behavior?
a. Ne
b. CH3Cl
c. Kr
d. CO2
e. F2
Short Answer
26. Explain why aerosol cans should not be left near a heater.
The increase in temperature will cause the volume of the gas to
increase.
Problem
27. Show the mathematical proof that R= .08206 Latm/Kmoles
Assume we have 2 moles of a gas at STP.
This means we have 44.8L
We will plug in PV=nRT and see what R is
P=1 atm V=44.8L n=2 moles T=273K
P
x V
= n
x R x T
(1atm) x (44.8L) = (2moles) x (R) x (273K)
R= (1 atm x 44.8 L)
(273 K x 2 moles)
R= 0.08206 atmL/molesK