Download - Lecture 7.2 - Liquids & Phase Changes
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States OfStates Of
Matter II:Matter II:
Liquid Properties & Phase ChangesLiquid Properties & Phase Changes
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q p gq p g
Liquid PropertiesLiquid Properties
Cohesive ForcesCohesive Forces the intermolecular
attraction between like molecules Adhesive ForcesAdhesive Forces the attraction
between unlike molecules
Water (red) hasstronger adhesive
forces. Mercury hasstronger cohesiveforces.
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H2O vs Hg
Adhesion
Cohesion
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Properties of LiquidsProperties of Liquids
1.Surface Tension
2.Capillary Action
3.Viscosity
4.Vapor Pressure
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Surface TensionSurface Tension
Surface tension is the amount of energy required to
stretch or increase the surface of a liquid by a unitarea.
Strong intermolecular forces
= High surface tension
- tendency to minimizesurface area
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Surface Tension Fun
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http://flickr.com/photos/72553346@N00/237875014/ -
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In Orbit (Space Shuttle), waterdroplets are spherical
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Water Boiling in ZeroGravity
http://science.nasa.gov/headlines/images/boiling/bubble0g.mpg
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http://www.unoriginal.co.uk/nuvideos1234/balloon%20-
%20UNORIGINAL.CO.UK.wmv
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Capillary ActionCapillary Action The ability of a liquid to flow against gravity up a narrow
tube.
Attraction of water to glass walls draws water up tubes 10
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ViscosityViscosity
measure of a fluids resistance to flow.
If a liquid has strong intermolecular
interactions then particles will not flow pasteach other easily and viscosity will be high.
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Viscosity of Several Hydrocarbons
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Viscosity of Some Common Liquids
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15Greatest Order
Least Order
Phase ChangesPhase Changes
Endo
thermic
Exoth
erm
ic
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Some Molecules in an open
beaker have enoughkinetic energy to vaporizefrom the surface of theliquid.
Vaporization
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A system at equilibrium is dynamic (changing) but
has no net macroscopic changes
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Vapor PressureVapor Pressure
The pressure exerted by a vapor in
equilibrium with its liquid phase.
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As IMF strength decreases, vapor pressure increases
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Volatile Liquids Liquids with high vapor pressures
They evaporate rapidly in an open dish
They have weak intermolecular forces
- more of its molecules can break free andvaporize
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As temperature increases, vaporpressure increases
- More molecules will have enoughKE to break away fromintermolecular forces
Vapor Pressure & TemperatureVapor Pressure & Temperature
T1 < T2 21
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Vapor Pressure Vs Temperature for Three Liquids
M l E th l f V i ti
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Hvap = energy required to vaporize 1 mole of a liquidat its boiling point (in kJ/mol)
Determined by the Clausius-Clapeyron Equation
Molar Enthalpy of Vaporization
( Hvap )
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Clausius-Clapeyron Equation
(equilibrium) vapor pressure= temperature (K)
gas constant (8.314 J/Kmol) 24
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or
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Alternate Forms of the Clausius-Clapeyron Equation
At two temperatures:
or
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Example Problem
Dry ice sublimes at 78oC andhas a H
subof 25.2 kJ/mol.
Calculate the vapor pressureof CO
2at 100oC.
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atmP
P
atm
P
atm
KK
KK
molKJ
molJ
P
atm
TT
TT
R
H
P
P
vap
vap
vap
vap
vap
vap
vap
138.0
23.710
00.1
859.000.1
log
)173)(195(
173195
)/31.8)(303.2(
/2520000.1log
303.2log
1
859.0
1
1
1
21
12
1
2
=
==
=
=
=
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A liquid boils when thermal energy is high enough to cause
molecules in the interior of the liquid to become gaseous,forming bubbles that rise to the surface.29
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The boiling pointis the temperature at which the
(equilibrium) vapor pressure of a liquid is equal to
the external pressure. (Pvap
= Patm
)
The normal boiling pointis the temperature at
which a liquid boils when the external pressure is 1
atm.
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H2O (s) H2O (l)
The melting pointof asolid or the freezing point
of a liquid is the
temperature at which the
solid and liquid phasescoexist in equilibrium
Solid-LiquidSolid-Liquid
EquilibriumEquilibrium
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Molar Enthalpy of Fusion ( Hfus )
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Hfus =is the energy (in kJ/mol) required to melt 1mole of a solid substance at its freezing point.
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HeatingHeating
CurveCurve
Energy input increases
Length of plateau depends
on Hvap
Length of plateau depends
on Hfus
Slope decreases as specific heat capacity of a phase increases
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AP Exam Diagrams
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H2O (s) H2O (g)
Molar heat ofsublimation ( Hsub )is the energy requiredto sublime 1 mole of a
solid. Hsub = Hfus + Hvap
( Hesss Law)
Solid-GasSolid-Gas
EquilibriumEquilibrium
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Aphase diagram summarizes the conditions at
which a substance exists as a solid, liquid, or gas.
Phase Diagramof Water
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Effect of Increase in Pressure on the Melting Point
of Ice and the Boiling Point of Water
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Phase diagram for CO2
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Triple point
A three-way intersection representing the
unique temp, pressure where all threephases exist simultaneously in equilibrium.
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Critical Point (Tc)
The temperature (critical temperature) where a gascannot be liquefied no matter what the pressure.
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The Critical Phenomenon of SF6
T < Tc T > Tc T ~ Tc T < Tc
Th iti l t t (T ) i th t t b hi h th
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The critical temperature (Tc) is the temperature above which the gas
cannot be made to liquefy, no matter how great the applied pressure.
The critical pressure(Pc) is the minimum
pressure that must be
applied to bring aboutliquefaction at the criticaltemperature.
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Supercritical fluid
Neither a liquid nor a gas. The liquidand gas forms becomeindistinguishable at this point.
http://www.nottingham.ac.uk/supercritical/scintro.
html
Ph di f H O
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Phase diagram for H2O
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Density of PhasesDensity of Phases
+ slope: dsolid > dliquid slope: dsolid < dliquid
most substances H2O
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AP Exam Diagram
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3 D Structure of Water
W t i U i S b t
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3-D Structure of Water
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Density of Water
Maximum
Density40C
Ice is less dense than water
Water is a Unique Substance
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Water
colorless, odorless, tasteless, liquid at ordinarytemperatures
only inorganic compound occurring naturally asa liquid
Composes ~65% of mass of living organisms excellent solvent for many things
abnormally high boiling and melting point
ice is less dense than water (it floats)
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Water purification
Hard water -- Contains Ca+2 , Mg+2 , Fe+3 and other minerals.
Soft water -- Doesnt contain Ca+2 , Mg+2 ,Fe+3 ions.
Softened water -- metal cations in hardwater are replaced by Na+.
Deionized water -- cations are replaced
by H+ and anions are replaced by OH-
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Chemistry In Action: Ice Skating
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Chemistry In Action: Ice Skating
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HomeworkHomework
p. 501 # 40c-f, 41, 42p. 501 # 40c-f, 41, 42p. 504 # 81, 82p. 504 # 81, 82 (use 250.0 g of substance X)(use 250.0 g of substance X)
p. 505 # 86 - 89p. 505 # 86 - 89