Properties of a Straight-line Graph
71
Because
2.303/? '
A//, = -(m)(2.303)(/O = -(-2.22 x 10'deg)(2.303) I 1.987
cal
mole
= +1.02 x 10
4 cal/mole
If you also want to findS, then choose a simple pressure, such as P = 100 torr (so
that logf = 2.000) and the corresponding value of 1/7 (it turns out to be 0.003075),
and substitute them into the basic equation along with the calculated value of the
slope (-2.22 x 10
! ), to give:
2.000 = (-2.22 x 10 ')(0. 003075) + B
B = 2.000 + 6.826 = 8.83
The general equation showing how the vapor pressure of water varies with temperature thus is
2220
log/
3 = - — + 8.83
340
320
300
280
260
240
CL
en
200
1 80
1 60
1 40
1 20
\
V
\ \'
0
\
5
i>
00
N
-0000
\ \
225->- \
\ s
\
27
28 29 30 31
32 33 34
FIGURE 6-5
y X 10 3