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Tulsi Mehta
Subject: Chemistry
, asked on 24/1/18
IS IT CORRECT ?
Difference between formation enthalpy and reaction enthalpy.
∆
f
H
→
1
f
o
r
m
e
d
f
r
o
m
c
o
n
s
i
t
u
e
n
t
e
l
e
m
e
n
t
2
1
m
o
l
e
o
f
p
r
o
d
u
c
t
i
s
f
o
r
m
e
d
.
∆
r
H
→
1
m
a
y
o
r
m
a
y
n
o
t
b
e
f
o
r
m
e
d
f
r
o
m
c
o
n
s
t
i
t
u
e
n
t
e
l
e
m
e
n
t
.
2
1
m
o
l
e
o
f
p
r
o
d
u
c
t
m
a
y
o
r
m
a
y
n
o
t
b
e
f
o
r
m
e
d
.
Answer
1
Tulsi Mehta
Subject: Chemistry
, asked on 24/1/18
Answer for the underlined question ?
A swimmer coming out from a pool is covered with a film of water weighing about 18g.
How much heat must be supplied to evaporate this water at 298K?
Calculate the internal energy of vaporisation at 100
°
C.
Answer
1
Tulsi Mehta
Subject: Chemistry
, asked on 24/1/18
In example 6.5 of ncert on pg 161,
In both cases there is no change in volume . Then why for conversion to gas we use formula delta U + nRt
And for conversion to ice we assume nRt =0?
Problem
6
.
5
If
water
vapour
is
assumed
to
be
a
perfect
gas
,
molar
enthalp
change
for
vapourisation
of
1
mol
of
water
at
1
bar
and
100
°
C
is
41
kJ
mol
-
1
.
Calculate
the
internal
energy
change
,
when
(
i
)
1
mol
of
water
is
vaporised
at
1
bar
pressure
and
100
°
C
.
(
ii
)
1
mol
of
water
is
converted
into
ice
.
Solution
:
(
i
)
The
change
H
2
O
(
l
)
→
H
2
O
(
g
)
△
H
=
△
U
+
△
n
g
RT
or
△
U
=
△
H
-
△
n
g
RT
,
substitutinh
the
values
,
we
get
△
U
=
41
.
00
kJ
mol
-
1
-
1
×
8
.
3
J
mol
-
1
K
-
1
×
373
K
=
41
.
00
kJ
mol
-
1
-
3
.
096
kJ
mol
-
1
=
37
.
904
kJ
mol
-
1
(
ii
)
The
change
H
2
O
(
l
)
→
H
2
O
(
s
)
There
is
negligible
change
in
volume
,
So
,
we
can
put
p
△
V
=
△
n
g
RT
≈
0
in
this
case
,
△
H
≅
△
U
so
,
△
U
=
41
.
00
kJ
mol
-
1
Answer
1
Tulsi Mehta
Subject: Chemistry
, asked on 24/1/18
Are these eqns on pg 160 applicable for free exapansion ?
E
q
u
a
t
i
o
n
6
.
1
,
△
U
=
q
+
w
c
a
n
b
e
e
x
p
r
e
s
s
e
d
f
o
r
i
s
o
t
h
e
r
m
a
l
i
r
r
e
v
e
r
s
i
b
l
e
a
n
d
r
e
v
e
r
s
i
b
l
e
c
h
a
n
g
e
s
a
s
f
o
l
l
o
w
s
:
1
.
F
o
r
i
s
o
t
h
e
r
m
a
l
i
r
r
e
v
e
r
s
i
b
l
e
c
h
a
n
g
e
q
=
-
w
=
p
e
x
V
f
-
V
i
2
.
F
o
r
i
s
o
t
h
e
r
m
a
l
r
e
v
e
r
s
i
b
l
e
c
h
a
n
g
e
q
=
-
w
=
n
R
T
ln
V
f
V
i
=
2
.
303
n
R
T
log
V
f
V
i
3
.
F
o
r
a
d
i
a
b
a
t
i
c
c
h
a
n
g
e
,
q
=
0
△
U
=
w
a
d
Answer
4
Ruchira Das
Subject: Chemistry
, asked on 9/1/18
how thermodynamic chapter is related to states of matter??
Answer
1
Shivam
Subject: Chemistry
, asked on 9/1/18
Q. 2 mole of zinc is dissolved in HCI at 25
°
C .Calculate the work done in open vessel.
Answer
1
Shivam
Subject: Chemistry
, asked on 9/1/18
please solve question 2
Answer
1
Shivam
Subject: Chemistry
, asked on 9/1/18
please solve question 1
Answer
2
Ayesha Jahan
Subject: Chemistry
, asked on 6/1/18
heat capacity of H2 at constant pressure and temperature
Answer
1
Adharsh
Subject: Chemistry
, asked on 4/1/18
17. Calculate the enthalpy of Hydrogenation of C
2
H
2
(g) to C
2
H
4
(g). (Bond energies given : C-H = 414.0 kJ mol
-1
, C
≡
C = 827.6 kJ.mol
-1
, C-C = 485.0 K) mol
-1
& H-H = 430.5 kJ mol
-1
)
Answer
1
Shivam Desale
Subject: Chemistry
, asked on 3/1/18
Qn no. 2
Answer
1
Shreya Choudhary
Subject: Chemistry
, asked on 3/1/18
Q. In which of the following reactions, standard reaction entropy change (
△
S
°
) is positive and standard Gibb's energy change
∆
G
°
decresases sharply with increasing temperature?
1
.
M
g
(
s
)
+
1
2
O
2
(
g
)
→
M
g
O
(
s
)
2
.
1
2
C
g
r
a
p
h
i
t
e
+
1
2
O
2
(
g
)
→
1
2
C
O
2
(
g
)
3
.
C
g
r
a
p
h
i
t
e
+
1
2
O
2
(
g
)
→
C
O
(
g
)
4
.
C
O
(
g
)
+
1
2
O
2
(
g
)
→
C
O
2
(
g
)
Answer
2
Shreya Choudhary
Subject: Chemistry
, asked on 3/1/18
Solve this :
4
.
F
o
r
t
h
e
r
e
a
c
t
i
o
n
,
X
2
O
4
l
→
2
X
O
2
g
∆
U
=
2
.
1
k
c
a
l
,
∆
S
=
20
c
a
l
K
-
1
a
t
300
K
H
e
n
c
e
,
∆
G
i
s
A
I
P
M
T
-
2014
1
2
.
7
k
c
a
l
2
-
2
.
7
k
c
a
l
3
9
.
3
k
c
a
l
(
4
)
-
9
.
3
k
c
a
l
Answer
1
Krithikha B
Subject: Chemistry
, asked on 31/12/17
Calculate the enthalpy change for hydrogenation of carbon if enthalpy of combustion of carbon, hydrogen and methane are -393.5, -285.8 and -890.3KJmol -1 .
Answer
1
Krithikha B
Subject: Chemistry
, asked on 31/12/17
Calculate the change in enthalpy and internal energy for the given reaction at 298K: C(s) + H2O(g) CO(g) + H2(g) given the standard enthalpy of formation of H2O and CO are -241.8 and -110.5 KJmol-1
here we dont have h20 standard enthapy...am stuck plz help
Answer
1
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What are you looking for?
Difference between formation enthalpy and reaction enthalpy.
A swimmer coming out from a pool is covered with a film of water weighing about 18g.How much heat must be supplied to evaporate this water at 298K? Calculate the internal energy of vaporisation at 100C.
In both cases there is no change in volume . Then why for conversion to gas we use formula delta U + nRt
And for conversion to ice we assume nRt =0?
Q. In which of the following reactions, standard reaction entropy change () is positive and standard Gibb's energy change decresases sharply with increasing temperature?
here we dont have h20 standard enthapy...am stuck plz help