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Gases and the Kinetic
Molecular Theory
Principles of General Chemistry, 2
nd
ed. By M. Silberberg
Chemistry, 8th ed.
by W. Whitten, R. Davis, R., M. L. Peck, and G. Stanley.
1. A steel tank used for fuel delivery is fitted with a safety
valve that opens if the internal pressure exceeds 1.00 x
10
3
torr.
It is filled with methane at 23
o
C and 0.991 atm
and placed in boiling water at exactly 100
o
C.
Will the
safety valve open?
Exercises
2. A scale model of a blimp rises when it is filled with
helium to a volume of 55.0 dm
3
.
When 1.10 mol of He is
added to the blimp, the volume is 26.2 dm
3
.
How many
more grams of He must be added to make it rise?
Assume constant
T
and
P
.
3. A steel tank has a volume of 438 L and is filled with
0.885 kg of O
2
.
Calculate the pressure of O
2
at 21
o
C.
Solutions
P
1
= 0.991 atm (convert to torr)
P
2
= unknown
T
1
= 23
o
C (convert to K)
T
2
= 100
o
C (convert to K)
P
1
T
1
P
2
T
2
=
0.991 atm x
1 atm
760 torr
= 753 torr
P
2
=
P
1
x
T
2
T
1
=
753 torr x
373 K
296 K
= 949 torr
1. V
and
n
remain constant and
Solutions
n
1
= 1.10 mol
n
2
= unknown (find, then subtract
n
1
)
V
1
= 26.2 dm
3
V
2
= 55.0 dm
3
2. P
and
T
are constant
V
1
n
1
V
2
n
2
=
n
2
=
n
1
V
2
V
1
n
2
= 1.10 mol x
55.0 dm
3
26.2 dm
3
= 2.31 mol He
n
add’l
= 2.31 mol He – 1.10 mol He = 1.21 mol He
1.21 mol He
Mass (g) of He
=
4.003 g He
1 mol He
=
4.84 g He
x
Solutions
3. V
= 438 L
T
= 21
o
C
(convert to K)
n
= 0.885 kg O
2
(convert to mol)
P
= unknown
21
o
C + 273.15 = 294 K
0.885 kg x
10
3
g
kg
mol O
2
32.00 g O
2
= 27.7 mol O
2
P
=
nRT
V
27.7 mol
294 K
atm•L
mol•K
0.0821
x
x
438 L
= 1.53 atm
6
MassVolume Relationships
in Reactions Involving Gases
(gas stoichiometry)
2 mol KClO
3
yields
2 mol KCl and 3 mol O
2
2(122.6g)
yields
2 (74.6g) and 3 (32.0g)
Those 3 moles of O
2
can also be thought of as:
3(22.4L) or 67.2 L at STP
g)
(
2
(s)
MnO
(s)
3
O
3
+
KCl
2
KClO
2
2
→
∆
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MassVolume Relationships in
Reactions Involving Gases
•
Example:
What
volume
of
oxygen
measured at STP, can be produced
by the thermal decomposition of 120.0
g of KClO
3
?
8
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This note was uploaded on 07/24/2011 for the course CHEM 16 taught by Professor Siao during the Spring '07 term at University of the Philippines Diliman.
 Spring '07
 SIAO
 Mole, Stoichiometry

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