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Byju's Answer
Standard XII
Chemistry
Heat of Formation
Given the fol...
Question
Given the following:
C
(
s
)
+
O
2
(
g
)
→
C
O
2
(
g
)
;
Δ
H
=
−
394
k
J
/
m
o
l
2
H
2
(
g
)
+
O
2
(
g
)
→
2
H
2
O
(
l
)
;
Δ
H
=
−
568
k
J
/
m
o
l
C
2
H
5
O
H
(
l
)
+
3
O
2
(
g
)
→
2
C
O
2
(
g
)
+
3
H
2
O
(
l
)
;
Δ
H
=
−
1058
k
J
/
m
o
l
Using the given data, the heat of formation of ethanol is:
A
−
582
k
J
/
m
o
l
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B
71.8
k
J
/
m
o
l
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C
−
244
k
J
/
m
o
l
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D
+
782
k
J
/
m
o
l
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Solution
The correct option is
C
−
582
k
J
/
m
o
l
heat of formation for ethnaol-
2
C
+
3
H
2
+
1
2
O
2
⟶
C
2
H
5
O
H
To get the enthalpy from the above reactions,
Multiply the first reaction and second reaction with
2
and
3
2
respectively and reverse the third reaction after that add all the enthalpies-
2
C
+
2
O
2
→
2
C
O
2
3
H
2
+
3
2
O
2
→
3
H
2
O
2
C
O
2
+
3
H
2
O
→
C
2
H
5
O
H
+
3
O
2
So the Formation enthalpy of ethanol=
2
×
394
−
3
2
×
568
+
1058
=
−
582
K
J
Suggest Corrections
0
Similar questions
Q.
Given that:
C
(
s
)
+
O
2
(
g
)
→
C
O
2
(
g
)
;
Δ
H
=
−
394
kJ and
2
H
2
(
g
)
+
O
2
(
g
)
→
2
H
2
O
(
l
)
,
Δ
H
=
−
568
kJ and
C
2
H
5
O
H
(
l
)
+
3
O
2
(
g
)
→
2
C
O
2
(
g
)
+
3
H
2
O
(
l
)
;
Δ
H
=
−
1058
kJ/mole. Using the data, the heat of formation of ethanol is:
Q.
Given that,
C
(
s
)
+
O
2
(
g
)
→
C
O
2
(
g
)
;
Δ
H
=
−
394
k
J
2
H
2
(
g
)
+
O
2
(
g
)
→
2
H
2
O
(
l
)
;
Δ
H
=
−
568
k
J
C
H
4
(
g
)
+
2
O
2
(
g
)
→
C
O
2
(
g
)
+
2
H
2
O
(
l
)
;
Δ
H
=
−
394
k
J
Heat of formation of
C
H
4
is :
Q.
C
(
s
)
+
O
2
(
g
)
→
C
O
2
(
g
)
;
Δ
H
=
−
94.3
kcal/mol
C
O
(
g
)
+
1
/
2
O
2
(
g
)
→
C
O
2
(
g
)
;
Δ
H
=
−
67.4
kcal/mol
O
2
(
g
)
→
2
O
(
g
)
;
Δ
H
=
117.4
kcal/mol
C
O
(
g
)
→
C
(
g
)
+
O
(
g
)
;
Δ
H
=
230.6
kcal/mol
Calculate
Δ
H
for
C
(
s
)
→
C
(
g
)
in Kcal/mol.
Q.
C
(
s
)
+
O
2
(
g
)
→
C
O
2
,
(
g
)
;
Δ
H
=
−
94.3
kcal/mol
C
O
(
g
)
+
1
2
O
2
(
g
)
→
C
O
2
(
g
)
;
Δ
H
=
−
67.4
kcal/mol
O
2
(
g
)
→
2
O
(
g
)
;
Δ
H
=
117.4
kcal/mol
C
O
(
g
)
→
C
(
g
)
+
O
(
g
)
;
Δ
H
=
230.6
kcal/mol.
Calculate
Δ
H
for
C
(
s
)
→
C
(
g
)
in kcal/mol.
Q.
Find the heat of formation of ethyl alcohol from following data
C
(
s
)
+
O
2
(
g
)
⟶
C
O
2
(
g
)
......
Δ
H
=
−
94
K
c
a
l
H
2
(
g
)
+
I
/
2
O
2
(
g
)
⟶
H
2
O
(
l
)
;....
Δ
H
=
−
68
K
c
a
l
C
2
H
5
O
H
(
l
)
+
3
O
2
(
g
)
⟶
2
C
O
2
(
g
)
+
3
H
2
O
(
l
)
.....
Δ
H
=
−
327
K
c
a
l
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