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> Figure 8. Constant-pressure heat capacity of H2O(l) and H2O(cr,I)
Standard-state entropy of liquid water at subzero temperatures
Standard-state entropy of NaCl(aq)
SR99_02
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Table
8.
Coefficients
to
Speedy's
(1987)
empirical
equations
for
calculating
the
thermophysical
properties
of
supercooled
water.
α
10
3
κ
T
C
p
(bar
1
)
1
mol
1
)
x
(K)
(J
K
C
x
0.80
20.0
14.2
B
x(0)
1.802 180 3
4.120
25.952
B
x(1)
0.941
698 0
1.130
128.281
B
x(2)
0.905 507 0
77.817
14.2
B
x(3)
0.80
78.143
221.405
B
x(4)
54.290
64.812
max
resid
1.2 ppm
0.2%
0.03%
ties
of
supercooled
water.
His
expression
for
the
constant-pressure
heat
capacity
of
supercooled
water
is
4
∑
B
Cn)
ε
n
+ 2
C
C
(
ε
1/2
C
p
=
(42)
p
p
n
=0
(0)
(4)
where
B
C
p
,K ,
B
C
p
and
C
C
p
are
fitted
coefficients.
The
estimated
values
of
these
coefficients
are
presented
in
Table
8. The
parameter
ε is a
reduced
temperature
T
T
s
=
T
,
T
s
being
a
limiting
temperature
that
is
assumed
to be
exactly
227.15
K
s
(46
C).
Figure
8 presents
the
constant-pressure
heat
capacity
of
water
as
calcu-
lated
by
the
models
of Hill
(1990)
and
Speedy
(1987).
The
entropy
changes of
supercooled
water
can be
calculated
by
evaluating
the
integral:
250
200
H
2
O(l)
150
100
50
H
2
O(cr,
I)
0
200
220
240
260
280
300
Temperature
(K)
Figure
8.
Constant-pressure
heat
capacity
of H
2
O(l)
and
H
2
O(cr,I)
under
p
=
0.101325
MPa
and
T
=
200
K to
300
K.
C
p
[H
2
O(cr,I)]
values
were
calculated
with
the
MaierKelly
model.
C
p
[H
2
O(l)]
values
between
T
=
200
K
and
273
K
were
calculated
with
Speedy's
(1987)
model.
C
p
[H
2
O(l)]
values
between
T
=
274
K
and
300
K
were
calculated
with
Hill's
(1990)
equation-of-state
model.
16
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