More Ch.6
TestQuestions
Ch. 6 AP
Name:
Period:
, is sometimes used as a rocket propellant.
4
1. Liquid hydrazine, N,H
for the formation of hydrazine from its elements and use the combustii
equation
a. Write an
equations below to derive an equation in which AHf° for liquid hydrazine is expressed in
.
3
2 and AR
, AH
1
terms of AH
1
AH
> NO
½ N2(g) +
g>
2
H2(g) + ½ °2(g) > H2°(g)
> 2
O(g)
H
(I) + 30
4
H
2
N
NO2(g) + 2
2(g)
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2 N iI4
b. In a rocket, liquid hydrazine is reacted with liquid hydrogen peroxide to produce nitrogen
and water vapor. Write a balanced equation for this reaction.
i ‘N. ft
Calculate AH° or the reaction represented in 2b.
AHf° kJ/ mol
50.6
)
1
(
4
H
2
N
—187.8
)
1
(
2
H,0
285.8
O(g)
2
H
-
.
4
4b tA’
4’o1
L 4’
4:
d. Calculate AH°r<n for the reaction in 2b using bond dissociation energies.
Bond Dissociation Energy kJ/ mol
0—0142
N—N 167
0=0494
N=N 418
0—H 459
NN 942
N-H386
4#
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w
,V-,v --iio zo- oJ
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-
w
e. Which value of AH° (that calculated in part c or part d) is likely to be more accurate?
Justify your answer.
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1
ra
4
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ictc
4
lit
)
i
1
4
(UL)-1
ted in
f. Calculate the maximum temperature of the combustion gases if all the energy genera
and
the reaction goes into raising the temperature of those gases. [The heat capacities of N2(g)
are 29.1 J/(mol.°C) and 33.6 J/(moL°C), respectively.I
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ass
w
/
A
/4
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Z417
AA1 33.6
a
29.1
29.14i)
33.6 f4T) /-(
(%j/rZ?w
iso 41 /
f: 163.5
k-’(
1
-?
z
r,9c-iO
tlT: 5.00
I
I
2. Coffee cup calorimetry experiments can be used to obtain AHf° for magnesium oxide.
a. Write a balanced equation for the formation of magnesium oxide, whose enthalpy change
IsAH°
with
b. To determine the heat capacity of the calorimeter, 49.6 mL of 1.01 M HC1 are reacted
the
ine
.
Determ
6.40°C
by
es
increas
50.1 mL of 0.998 M NaOH. The solution’s temperature
is 4.025
heat capacity of the calorimeter. You may assume the solution’s specific heat capacity
0 and the solutions have a
3
1 °C, the enthalpy of neutralization is —55.9 kJ per mole of H
fg
density of 1.0 g/mL
I
h
c
t
t%&#7
I
=
‘
-
-
to C
?
2f6i i&
2
/
I
2z
Z
%S
.
/
c. When 0.221 g of magnesium turnings are added to 49.9 mL of 1.01 M HC1 and 49.7 mL of
1-190 in the same calorimeter, the temperature increases by 9.67°C. Write a balanced equatiou
for the reaction that occurs and calculate the zSH per mole magnesium. (Assume the solution’s
1 and the heat capacity of the calorimeter is the value
specific heat capacity is 3.862 JOg’ °C
obtained in b.)
o,oD
c1
fei
,o6oj-
?
&o7&f
Zz9s
.1z1z
3
&,C091Y
I,62’Ui i10 in the same
2
d. When 0.576 g of MgO react with 51.0 mL of 1.01 M HC1 and 50.1 mL of H
calorimeter the temperature rises 4.72°C. Write a balanced equation for this reaction and
calculate its Al-I per mole of MgO using the same assumptions as in part c.
t
/t(
?Zz
4hL
:
If
) to calculate Al-If° of magnesium
1
° of H,0(j) (—85.8 kJmo1
1
e. Use the above results and Al-1
oxide.
j
j:O-’7
C
4
L/
4 h’ Z
4 1q :
-
*
is
L—