# Thermodynamics Review

Mechanics

Oct 27, 2013 (4 years and 8 months ago)

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___
__________________________

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1

Thermodynamics

Review

1
. The complete comb
ustion of pent
ane gas, C
5
H
12

in oxygen gas produces CO
2

and H
2
O. It
is a highly exothermic process releasing
3123

kJ of heat per mole of
pent
ane. Write the
balanced thermochemical equation using all whole
-
num
ber coefficients. Also determine the
enthalpy c
hange in burning 65

g of
pent
ane gas.

3.
A reaction is performed in which 50.0 ml of 0.
4
00 M silver nitrate and
75
.0 ml of 0.100
M hydrochloric acid are mixed together. The initial temperature of th
e solution was
25.0
o
C and the final temperature was
27.2
o
C. Determine the enthalpy, in kJ/mol, for the
formation of the precipitate

(silver chloride)
. The volume of the final solution was 1
25

ml,
and it had a density of 1.00 g/ml. The specific heat of w
ater is 4.18 J/g
o
C.

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4. A 2.50 kg piece of copper metal is heated from 25.0
o
C to 225.0
o
C. How much heat, in
kJ, is absorbe
d by the copper? The specific
heat of copper is 0.384 J/g
o
C.

5. Determine the standard enthalpy of reaction for the combus
tion of hydrogen sulfide
gas, which proceeds according to the following reaction:

2 H
2
S
(g)

+ 3O
2
(g)

2 H
2
O
(l)

+ 2 SO
2
(g)

Formula

H
o
f

(kJ/mol)

H
2
S
(g)

-
20

H
2
O
(l)

-
285.8

SO
2
(g)

-
296.8

6. Determine the entropy change,

S
o
, for this re
action. The standard molar entropy
values are: H
2
(g)

= 130.6 JK
-
1
; O
2
(g)

= 205.0 JK
-
1
; H
2
O
(l)

= 69.9 JK
-
1
;

2 H
2
(g)

+ O
2
(g)

2

H
2
O
(l)

7.
Predict whether the following reaction is spontaneous
if it occurs at a temperature of
20
o
C and
if

S =
102.2 j/mol K
and

H =
-
32.5 kj/mol
.

N
2
(g)

+ 3 H
2
(g)

2 NH
3
(g)

8. Acetylene gas, C
2
H
2
, is used in gas welding procedures and is a very important
commercial gas. Use the data below to answer the following questions about the
combustion
of acetylene gas.

Substance

H
o
f
(kJ mol
-
1
)

S
o

(J mol
-
1

K
-
1
)

C
2
H
2

227

200.9

O
2

0

205.0

CO
2

-
393.5

213.7

H
2
O

-
285.8

69.9

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___
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Use the data above to answer the questions that follow. Assume that all reactions
occur at 25
o
C.

a)

Write the complete balanced che
mical equation for the combustion of acetylene.
Assume that carbon dioxide and water are the only products.

b)

Calculate the standard enthalpy change,

H
o
, for the combustion of acetylene.

c)

Calculate the standard entropy change,

S
o
, for the combustion of

acetylene.

d)

Determine the value for

G
o

for the reaction.

e)

If 1.0 mole

of acetylene is burned and all of the heat produced is used to heat a
6.00 kg sample of pure water, what will the temperature change of the water be?
The specific heat of water is 4
.18
J g
-
1

K
-
1
.

10. The specific heat of lead metal, Pb is 0.127
J g
-
1

K
-
1
.
How many joules of heat would be
required to raise the temperature of a 5.00 g sample from 25
o
C

to 3
5
o
C
.

a)

2.5 x 10
-
3

b)

0.127

c)

6.4

d)

1.61 x 10
1

e)

3.94 x 10
3

11.
Which of the followi
ng reactions involves the largest increase in entropy?

a)

AgNO
3
(aq)

+ HCl
(aq)

AgCl
(s)

+ HNO
3
(aq)

b)

N
2
(g)

+ O
2
(g)

2 NO
(g)

c)

2 NO
(g)

+ O
2
(
g
)

2

NO
2
(g
)

d)

2 KClO
3
(s)

2 KCl
(s)

+ 3 O
2
(g)

e)

2 SO
2
(g)

+
O
2
(g)

2 SO
3
(g)