segal (mas6582) – H12: Thermo 1 – mccord – (50970)
1
This
printout
should
have
19
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
10.0 points
On January 1, 2001, a bookstore had 266,478
books in stock. On February 1, 2001, the same
bookstore had 257,814 books in stock. What
is the value of Δ(books) for the bookstore
during that period?
Correct answer:

8664 books.
Explanation:
B
f
= 257
,
814 books
B
i
= 266
,
478 books
Δ
B
=
B
f

B
i
= 257
,
814 books

266
,
478 books
=

8664 books
Thus the bookstore had 8664 fewer books
on February 1.
002
10.0 points
Work is
1.
kinetic energy.
2.
heat.
3.
chaotic molecular motion.
4.
potential energy.
5.
organized molecular motion.
correct
Explanation:
Work is organized molecular motion since
it is displacement of a solid against a force.
003
10.0 points
A chemical reaction takes place in a container
of crosssectional area 100 cm
2
. As a result of
the reaction, a piston is pushed out through 10
cm against an external pressure of 557 torr.
What is the value for
w
for this reaction?
(Sign does matter.)
Correct answer:

74
.
3 J.
Explanation:
004
10.0 points
A 100 W electric heater (1 W = 1 J
/
s) oper
ates for 10
.
5 min to heat the gas in a cylinder.
At the same time, the gas expands from 4 L to
13 L against a constant atmospheric pressure
of 3
.
937 atm. What is the change in internal
energy of the gas?
Correct answer: 59
.
4098 kJ.
Explanation:
P
ext
= 3
.
937 atm
V
ini
= 4 L
1 L
·
atm = 101
.
325 J
V
final
= 13 L
If the heater operates as rated, then the to
tal amount of heat transferred to the cylinder
will be
q
= (100 J
/
s) (10
.
5 min) (60 s
/
min)
= 63000 J = 63 kJ
Work will be given by
w
=

P
ext
Δ
V
in this case because it is an expansion against
a constant opposing pressure:
w
=

(3
.
937 atm) (13 L

4 L)
=

35
.
433 L
·
atm
Convert to kilojoules (kJ)
w
= (

35
.
433 L
·
atm)(101
.
325J
/
L
·
atm)
=

3590
.
25 J =

3
.
59025 kJ
The internal energy change is
Δ
U
=
q
+
w
= 63 kJ + (

3
.
59025 kJ)
= 59
.
4098 kJ
005
10.0 points
A system had 150 kJ of work done on it and
its internal energy increased by 60 kJ. How
much energy did the system gain or lose as
heat?
1.
The system gained 60 kJ of energy as
heat.
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segal (mas6582) – H12: Thermo 1 – mccord – (50970)
2
2.
The system lost 90 kJ of energy as heat.
correct
3.
The system gained 90 kJ of energy as
heat.
4.
The system lost 210 kJ of energy as heat.
5.
The system gained 210 kJ of energy as
heat.
Explanation:
Δ
U
=
q
+
w
q
= Δ
U

w
= 60 kJ

(+150 kJ)
=

90 kJ
(Negative means the system lost energy as
heat.)
006
10.0 points
When 2.00 kJ of energy is transferred as heat
to nitrogen in a cylinder fitted with a piston
at an external pressure of 2.00 atm, the nitro
gen gas expands from 2.00 to 5.00 L against
this constant pressure.
What is Δ
U
for the
process?
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 Fall '08
 wandelt
 Chemistry, Enthalpy, Energy, kJ/mol rxn

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