vapor pressure evaporation h 2 o(g) molecules (water vapor) h 2 o(l) molecules
TRANSCRIPT
Evaporation
H2O(g)molecules
(water vapor)
H2O(l)molecules
Evaporation
H2O(g)molecules
(water vapor)
H2O(l)molecules
Evaporation
H2O(g)molecules
(water vapor)
H2O(l)molecules
How Vapor Pressure is Measured
1 atm = 760 mm Hg
760 mm + 120 mm = 880 mm Hg
Animation by Raymond ChangAll rights reserved
Manometer Atmospheric Pressure
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 401
Manometer A
BIG = small + height
________ = small + __________
760 mm Hg
h = 120 mm
760 mm 120 mm
Small = 640 mm Hg
?
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 401
Manometer B
BIG = small + height
BIG = ________ + _________ 760 mm 120 mm
BIG = 880 mm Hg
760 mm Hg
h = 120 mm
?
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 401
The Manometer and Vapor Pressure
Barometer & Manometer
atmospheric pressure = 101.3 kPa
atmospheric pressure = 100.4 kPa
atmospheric pressure = 101.7 kPa
confinedgas
confinedgas
confinedgas
600 mm
200 mm325 mm
150 mm 100 mm
500 mm
750 mm
(a) (b) (c) (d)
Pressure and TemperatureSTST
PP (Standard Temperature and Pressure)
standard temperature standard pressure1 atm101.3 kPa760 mm Hg
273 K0oC
Equations / Conversion Factors:
K = oC + 273oC = K – 273
1 atm = 101.3 kPa = 760 mm Hg
Convert 25oC to Kelvin.
K = oC + 273
How many mm Hg is 231.5 kPa?
How many kPa is 1.37 atm?
25oC + 273 298 K=
X kPa = 1.37 atm101.3 kPa
1 atm= 138.8 kPa
X mm Hg = 231.5 kPa760 mm Hg
101.3 kPa= 1737 mm Hg
Pa
CONFINEDGAS
AIRPRESSURE
Hg HEIGHTDIFFERENCE
manometermanometer:: measures the
pressure of a confined gas
higherpressure
101.3 kPa
Atmospheric pressure is 96.5 kPa;mercury height difference is 233 mm.
Find confined gas pressure, in atm.
SMALL + HEIGHT = BIGSMALL + HEIGHT = BIG
0.953 atm + 0.307 atm = X atm
X = 1.26 atm
96.5 kPa1 atm
+ 233 mm Hg760 mm Hg
1 atm= X atm
96.5 kPa + 233 mm Hg = X atm
233 mm Hg
96.5 kPa
X atm
BIG
small
1.26 atm
Vapor Pressure
more“sticky”
less likely tovaporize
In general:LOW v.p.
not very“sticky”
more likely tovaporize
In general:HIGH v.p.
measure of the tendency for liquid particles to enter gas phase at a given temp.
a measure of “stickiness” of liquid particles to each other
NOT all liquids have same v.p. at same temp.
0 20 40 60 80 1000
20
40
60
80
100
TEMPERATURE (oC)
PRESSURE (kPa)
CHLOROFORM
ETHANOL
WATER
Volatile substances evaporate easily (have high v.p.’s).
BOILING when vapor pressure = confining pressure (usually from atmosphere)
b.p. = 78oC
b.p. = 100oC
atmospheric pressure is 101.3 kPa
Vapor Pressure
93.3
80.0
66.6
53.3
40.0
26.7
13.3
0 10 20 30 40 50 60 70 80 90 100
61.3oC 78.4oC 100oC
chlo
rofo
rm
ethy
l alc
ohol
water
Pre
ssur
e (K
Pa)
Temperature (oC)
101.3
ETHANOL
WATER
AIR PRESSURE(~100 kPa)
VAPORPRESSURE
(~5 kPa)
VAPORPRESSURE
(~10 kPa)
BOILING when vapor pressure = confining pressure (usually from atmosphere)
At sea level and 20oC…
ETHANOL
WATER
NETPRESSURE
(~95 kPa)
NETPRESSURE
(~90 kPa)
Water Molecules in Liquid and
Steam
Microscopic view of a liquid near its surface
The high energymolecules escapethe surface.
Behavior of a liquid in a closed container
Water rapidly boiling on a stove
Copyright © 2006 Pearson Benjamin Cummings. All rights reserved.
Pressure Cooker
120oC
Formation of a bubble is opposed by the pressure of the atmosphere
Zumdahl, Zumdahl, DeCoste, World of Chemistry 2002, page 452
Vapor Pressure
93.3
80.0
66.6
53.3
40.0
26.7
13.3
0 10 20 30 40 50 60 70 80 90 100
61.3oC 78.4oC 100oC
chlo
rofo
rm
ethy
l alc
ohol
water
Pre
ssur
e (K
Pa)
Temperature (oC)
101.3
Boiling Point and Pressure
Heating / Cooling Curve of Water
140
120
100
80
60
40
20
0
-20
Tem
pera
ture
(oC
)
Heat added at a constant rate
liquid water
water and steam
steam
ice andwater
ice
Heatin
g
Cooling
Gas Collected Over Water
Measuring the Vapor Pressure of a Liquid
Davis, Metcalfe, Williams, Castka, Modern Chemistry, 1999, page 376
Gas Mixtures and Dalton’s
Law
Gases Dissolved in Liquids