Answers to
PILOT Exam Nr 3
(Chapters 5 and 6)
Pts
1. When volume of the gas is constant, which of the following is true?
a) P
.
T = const.
b) P
.
V = const.
c) P + T = const.
d) P/T = const.
[4]
Use: (P
1
.
V
1
/ T
1
) = (P
2
.
V
2
/ T
2
)
apply V
1
= V
2
and see what appears to be constant
or use (P
.
V/T) = const., join V to the constant and see what is left as constant.
2. If we increase temperature of the gas from 50
o
C to 100
o
C at constant pressure then its volume will
a) increase twice
b) increase less than twice
c) decrease twice
c) decrease less than twice
[4]
You need to express temperature in Kelvins !
3. If we decrease volume of the ideal gas from 6 L to 3 L
at a constant temperature its pressure will
a) increase twice
b) increase less than twice
c) decrease twice
c) decrease less than
[4]
Use: P
.
V = const
or
(P
1
.
V
1
/ T
1
) = (P
2
.
V
2
/ T
2
)
and substitute V
1
= 6L V
2
= 3L. Find P
2
setting T
1
= T
2
4. A gas occupies volume 3 L at 300 K. What is its volume at 400 K if pressure is constant?
a) 2 L
b) 4 L
c) 6 L
d) 8 L
[4]
Use: (P
1
.
V
1
/ T
1
) = (P
2
.
V
2
/ T
2
)
apply P
1
= P
2
Substitute V
1
= 3 L
T
1
= 300 K
T
2
= 400 K so V
2
=
..
5. 32 g of methane (CH
4
) should occupy at STP conditions the volume closest to
a) 11.2 L
b) 22.4 L
c) 33.6 L
d) 44.8 L
[4]
Evaluate: 32 g of CH
4
make 32/16 mole. One mole has a volume 22.4 L so 2 moles have volume 44.8 L
6. 40 g of methane (CH
4
) was burned in oxygen to give CO
2
and water.
a) Write and balance the reaction
[4]
CH
4
+ 2O
2
→
CO
2
+ 2H
2
O
b) Calculate the volume of CO
2
that could be obtained by
burning 40 g of
methane
[8]
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 Winter '08
 Polaski
 Chemistry, Atom, Hydrogen Bond, Mole, Solubility

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