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Byju's Answer
Standard XII
Chemistry
Heat of Reaction
Heat of disso...
Question
Heat of dissociation for
H
2
O
in
H
+
and
O
H
−
ions is :
A
-57.27 kJ/mol
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B
+57.27 kJ/mol
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C
-50 kJ/mol
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D
+50 kJ/mol
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Solution
The correct option is
B
+57.27 kJ/mol
Heat of neutralisation :
H
+
+
O
H
−
⟶
H
2
O
;
Δ
H
=
−
13.7
×
4.18
k
J
=
−
57.27
k
J
Heat of dissociation of
H
2
O
into
H
+
and
O
H
−
will be positive.
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Similar questions
Q.
Calculate the lattice energy of a salt
M
X
(
s
)
from the data given below:
Heat of formation of
M
X
(
Δ
H
)
=
−
550
kJ/mol
Heat of sublimation of
M
(
S
)
=
80
kJ/mol
Heat of dissociation of
X
2
(
D
)
=
155
kJ/mol
Ionization energy of
M
(
I
)
=
347
kJ/mol
Electron affinity of
X
(
E
)
=
−
343
kJ/mol
Q.
Consider the following data:
Δ
f
H
∘
(
N
2
H
4
,
l
)
=
50
kJ/mol
,
Δ
f
H
∘
(
N
H
3
,
g
)
=
−
46
kJ/mol
,
B
.
E
(
N
−
H
)
=
393
kJ/mol
and
B
.
E
(
H
−
H
)
=
436
kJ/mol
,
Δ
v
a
p
H
(
N
2
H
4
l
)
=
18
kJ/mol
. Calculate the N-N bond energy in kJ/mol for
N
2
H
4
.
Q.
Bond dissociation enthalpies of
H
2
(
g
)
a
n
d
N
2
(
g
)
are
436.0
k
J
m
o
l
−
1
and
941.3
k
J
m
o
l
−
1
respectively. Enthalpy of formation of
N
H
3
(g) is
−
46.0
k
J
m
o
l
−
1
. What is the enthalpy of atomization of
N
H
3
.
Q.
The enthalpies of formation of
O
H
(
g
)
,
H
(
g
)
and
O
(
g
)
are 21
k
J
m
o
l
−
1
, 109
k
J
m
o
l
−
1
and 124
k
J
m
o
l
−
1
.
The value of bond enthalpy
O
−
H
is
Q.
What is the heat of formation of liquid methyl alcohol in
k
J
m
o
l
−
1
,
use the following data.
Heat of vaporization of liquid methyl alcohol =
38
k
J
m
o
l
−
1
.
Heat of formation of gaseous atoms from the elements in their standard states:
H
=
218
k
J
m
o
l
−
1
,
C
=
715
k
J
m
o
l
−
1
,
O
=
249
k
J
m
o
l
−
1
Average bond energies :
C
−
H
=
415
k
J
m
o
l
−
1
C
−
O
=
356
k
J
m
o
l
−
1
O
−
H
=
463
k
J
m
o
l
−
1
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