The effect of applied pressure on vapor pressure
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Transcript of The effect of applied pressure on vapor pressure
The effect of applied pressure on vapor pressure
rises. pressure vapour its phase,
condensed a toapplied is pressureWhen
ln (l)
(l)
(v) (l)
equili. preserves that changeany For
)()(
m,equilibriuAt
1
2
p
pRTPV
dpp
RTdPV
dd
gl
m
m
There is a relation between dp and dT that ensures that the system remains in equilibrium as either variable is changed.
The location of phase boundaries
Pressure and temperature at which two phases can coexist.
Relation between dp and dT
equation) (Clapeyron
),(),(
equal. still are
but changes potentials chemical theb,At
),(),(
,,,,
,,,,
V
S
dT
dp
dpSSdTVV
dpVdTSdpVdTS
dd
TpTp
TpTp
trs
trs
mmmm
mmmm
bb
aa
The solid –liquid boundary
curve Steep
large ve,
smallbut ve
ve
VT
H
dT
dp
fus
fus
Liquid –Vapour boundary
small ve,
large ve,
ve
VT
H
dT
dp
vap
vap
Equation)Clapeyron (Clausius
ln
(g)
2RT
H
dT
pd
p
RTT
H
dT
dp
VV
vap
vap
mvap
Solid-Vapour Boundary
vap-liquidan Steeper th
ve
large ve,
ve
VT
H
VT
H
dT
dp
vap
vap
sub
sub
1 bar
PF
PCF
3
system,component oneFor
2
Phase Rule
F=C-P+2
C = number of component
Total number of intensive variable = pc +2
Mole fraction of components in each phase must be one
Number of relation =number of phases= p
For chemical equilibrium,
Chemical potential of individual component will be same in each of the phases.
In each of the component
(p-1) relation for each of the component
Total number of relation for chemical equilibrium = c(p-1)
Degree of Freedom = pc + 2 – p - c(p-1)
= c – p + 2
.......1111
What happens to boiling point or freezing point of a liquid in the presence of a solute?
What happens to chemical potential of a liquid in the presence of solute?
solute. volatile-non ofaddition on
decreases liquid a of potential Chemical
) law s(Raoult' ln
ln
ln
(g) (l)
solute a of presenceIn
ln
(g) (l)
solvent pureFor
*
AAAA
AAA
AAA
AA
AAA
AA
xppxRT
p
pRT
pRT
pRT
There is elevation of boiling point upon addition of a solute.
There is depression of freezing point upon addition of a solute.
The elevation of boiling point
solvent.
theofconstant picebulliosco called is
)( 1
Where
2*
2*
b
Bb
ABvap
f
bAB
BA
BB
vap
Bf
K
mK
MmH
RTT
molalitymMmm
M
mx
H
RTK
KxT
1
(l) -(g) ln
ln (l) (g)
(l) (g)
T
TH
T
HTH
STHG
RT
G
RTx
xRT
vap
vapvap
vapvapvap
vapAAA
AAA
AA
Bvap
vapvapB
vapB
vapB
vapB
xH
RTT
T
T
R
H
TT
TT
R
Hx
TTR
Hx
TTR
Hx
TTR
Hx
2
2
11
11
111ln
The depression of Freezing point
constant. cryoscopic called is f
Bf
B
K
mKT
xKT
Solubility
TTR
Hx fusB
11ln
*
Solutes with high melting points and large enthalpies of melting have low solubilities at normal temperature.
Two component liquid Systems
ABAB
BAAA
BBAABA
BBB
AAA
xppp
pxpxp
pxpxppp
pxp
pxp
*
*
*
*
)1(
F=C-P+2 F=4-P
Maximum degree of freedom = 3
Temperature, pressure and composition.
ABAA
BA
ABAA
BAA
AABAAABA
ABAB
AAA
AA
yppp
ppp
yppp
pyx
yxpppxpy
xppp
pxy
p
py
Q. One mole of benzene is mixed with two moles of toluene. At 60 C , the vapor pressure of benzene and toluene are 51.3 and 18.5 kPa, respectively. (a) As the pressure is reduced, at what pressure will boiling begin? (b) What will be the composition of the first bubble of vapor?
581.0
4.29
p
py
kPaxpxpp
AA
BBAA