Copyright © Glencoe/McGraw-Hill, a division of The McGraw-Hill Companies, Inc.
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
135
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 13
Substitute the known quantities and calculate P.
P ϭ
ϭ
ϭ40.5 atm
Notice that this pressure makes sense because a large amount of gas
is being squeezed into a much smaller space.
Practice Problems
17. What is the pressure in atmospheres of 10.5 mol of acetylene in
a 55.0-L cylinder at 37°C?
18. What volume does 0.056 mol of H 2 gas occupy at 25°C and
1.11 atm pressure?
19. A sample of carbon monoxide has a volume of 344 mL at 85°C
and a pressure of 88.4 kPa. Determine the amount in moles of
CO present.
Using Mass with the Ideal Gas Law Recall that it is possible to
calculate the number of moles of a sample of a substance when you
know the mass of the sample and the formula of the substance.
number of moles (n) ϭ
; n ϭ
You can substitute this expression into the ideal gas law equation in
place of n.
PV ϭ nRT; PV ϭ
RT; or PVM ϭ mRT
Notice that this equation enables you to determine the molar mass of
a substance if you know the values of the other four variables.
Example Problem 13-6
Determining Molar Mass
Determine the molar mass of an unknown gas if a sample has a mass
of 0.290 g and occupies a volume of 148 mL at 13°C and a pressure
of 107.0 kPa.
First, convert the temperature to kelvins.
13°C ϭ (13 ϩ 273) K ϭ 286 K
m
ᎏ
M
m
ᎏ
M
mass of substance in grams
ᎏᎏᎏ
molar mass of substance
▲
18.6 mol ϫ 0.0821ᎏ
m
L и
o
a
l и
tm
K
ᎏ ϫ 318 K
12.00 L
nRT
ᎏ
V
Solving Problems: A Chemistry Handbook
Chemistry: Matter and Change
135
SOLVING PROBLEMS:
A CHEMISTRY HANDBOOK
CHAPTER 13
Substitute the known quantities and calculate P.
P ϭ
ϭ
ϭ40.5 atm
Notice that this pressure makes sense because a large amount of gas
is being squeezed into a much smaller space.
Practice Problems
17. What is the pressure in atmospheres of 10.5 mol of acetylene in
a 55.0-L cylinder at 37°C?
18. What volume does 0.056 mol of H 2 gas occupy at 25°C and
1.11 atm pressure?
19. A sample of carbon monoxide has a volume of 344 mL at 85°C
and a pressure of 88.4 kPa. Determine the amount in moles of
CO present.
Using Mass with the Ideal Gas Law Recall that it is possible to
calculate the number of moles of a sample of a substance when you
know the mass of the sample and the formula of the substance.
number of moles (n) ϭ
; n ϭ
You can substitute this expression into the ideal gas law equation in
place of n.
PV ϭ nRT; PV ϭ
RT; or PVM ϭ mRT
Notice that this equation enables you to determine the molar mass of
a substance if you know the values of the other four variables.
Example Problem 13-6
Determining Molar Mass
Determine the molar mass of an unknown gas if a sample has a mass
of 0.290 g and occupies a volume of 148 mL at 13°C and a pressure
of 107.0 kPa.
First, convert the temperature to kelvins.
13°C ϭ (13 ϩ 273) K ϭ 286 K
m
ᎏ
M
m
ᎏ
M
mass of substance in grams
ᎏᎏᎏ
molar mass of substance
▲
18.6 mol ϫ 0.0821ᎏ
m
L и
o
a
l и
tm
K
ᎏ ϫ 318 K
12.00 L
nRT
ᎏ
V