cha (dyc97) – Homework 11 – Sutcliffe – (53770)
1
This
printout
should
have
30
questions.
Multiplechoice questions may continue on
the next column or page – find all choices
before answering.
001
10.0 points
The
combustion
of
a
certain
amount
of
methane gives off 100 kJ of energy.
Dur
ing this process the amount of energy in the
universe
1.
The answer cannot be determined with
out knowing the heat capacity of methane.
2.
increases by 100 kJ.
3.
decreases by 100 kJ.
4.
does not increase or decrease.
correct
Explanation:
The First Law of Thermodynamics states
that the total amount of energy in the uni
verse is constant. The energy change occurs
in the system.
002
10.0 points
How much total work is done when 6
.
3 of H
2
expands from 25 liters to 50 liters against a
constant external pressure of 1 atm, then ex
pands further from 50 to 100 liters against a
constant external pressure of 0.1 atm?
An
swer in calories.
Correct answer:

726.
Explanation:
w
=

P
Δ
V
w
is not a state function. The pathway must
be taken into consideration. Calculate
w
for
each step.
Step 1
:
P
= 1 atm
V
i
= 25 L
V
f
= 50 L
Δ
V
= 25 L
w
= (

1 atm)(25 L)
parenleftbigg
101
.
33 J
atm
·
L
parenrightbigg
×
parenleftbigg
1 cal
4
.
1867 J
parenrightbigg
=

605
.
0708 cal
Step 2
:
P
= 0
.
1 atm
V
i
= 50 L
V
f
= 100 L
Δ
V
= 50 L
w
=

(0
.
1 atm)(50 L)
parenleftbigg
101
.
33 J
atm
·
L
parenrightbigg
×
parenleftbigg
1 cal
4
.
1867 J
parenrightbigg
=

121
.
0142 cal
summationdisplay
w
=

605
.
0708 cal

121
.
0142 cal
=

726
.
085 cal
003
10.0 points
An ideal gas is allowed to expand isothermally
from 2.00 liters at 5.00 atm to 5.00 liters at
2.00 atm against a vacuum (
i.e.
, no outside
pressure). Which of the quantities
q
,
w
, Δ
E
,
and Δ
H
are zero for this process?
1.
w
,
q
, and Δ
E
2.
w
3.
w
and Δ
E
,
4.
Some other combination
5.
w
,
q
, Δ
E
, and Δ
H
correct
Explanation:
P
= 0 so
w
=

P
Δ
V
= 0
.
For
isothermal
expansion,
T
=
const.
There is no change in molecular kinetic en
ergy or potential energy due to intermolecu
lar attraction (which is zero for ideal gases).
Therefore Δ
E
= 0.
Δ
E
=
q
+
w
0 =
q
+ 0;
q
= 0
Δ
H
=
q
= 0
Therefore
w
,
q
, Δ
E
, and Δ
H
all equal zero.
004
10.0 points
This preview has intentionally blurred sections. Sign up to view the full version.
View Full Document
cha (dyc97) – Homework 11 – Sutcliffe – (53770)
2
Which of the following is true of a general
thermodynamic state function?
1.
The change in the value of a state func
tion is always negative for a spontaneous re
action.
2.
The change of the value of a state func
tion is independent of the path of a process.
correct
3.
The value of the state function remains
constant.
4.
The change in the value of the state func
tion is always positive for endothermic pro
cesses.
5.
The value of a state function does NOT
change with a change in temperature of a
process.
Explanation:
A change in a state function describes a
difference between the two states. It is inde
pendent of the process or pathway by which
the change occurs.
005
10.0 points
For a certain reaction at constant pressure,
Δ
U
=

70 kJ, and 51 kJ of expansion work
is done by the system. What is Δ
H
for this
process?
This is the end of the preview.
Sign up
to
access the rest of the document.
 Fall '07
 Fakhreddine/Lyon
 Thermodynamics, Enthalpy, Energy, kJ/mol, Cha

Click to edit the document details