Transcript Change of State - Bergen County Technical Schools

Announcements
 1st HW answer key available Friday
afternoon
 LTEF poster due by 4:00 pm 10/1
 2nd HW due on 10/8 or 10/9
 Test on 10/11 or 10/12
Change of State
Vapor Pressure
What is Vaporization?
 aka Evaporation
 Change of state: liquid to gas
Is Evaporation Exo- or
Endothermic?
 Endothermic…why?
 Must overcome the intermolecular
forces
 DH(vap) for H2O is 40.7 kJ/mol
Practical Uses for Vaporization
 Most of the energy from the sun is
used to evaporate water rather than
warm the planet.
 Evaporation cools the human body.
What is the opposite of
vaporization?
 Condensation
 Rate of evaporation vs.
condensation
Vapor Pressure
 Pressure of the vapor above a
liquid when the rate of evaporation
and condensation are equal.
Measuring Vapor Pressure
Measuring Vapor Pressure
 Different liquids have different vapor
pressures. Why?
 How does temperature affect vapor
pressure?
Temperature vs. Vapor Pressure
 As T increases,
For H2O:
T (ºC)
0.0
25.0
40.0
70.0
90.0
P(torr)
4.58
23.76
55.32
233.7
525.8
vapor pressure
increases
 What happens when
T gets 100ºC?
 Boiling point: T at
which the vapor
pressure equals atm
pressure.
Graphing Pvap vs. Temperature
Chemistry and Straight Lines
Chemistry and Straight Lines
 Slope: - DHVAP / R
 lnP = [-DH / R][1/T] + b
 lnPT1 – lnPT2 = [DH / R][1/T2 – 1/T1]
Clausius Clapeyron Equation
ln[PT1 / PT2] = [DH / R][1/T2 – 1/T1]
Practice Problem
 The vapor pressure of water at
25ºC is 23.8 torr and the heat of
vaporization is 40.7 kJ/mol.
Calculate the vapor pressure of
water at 50ºC.
Heating Curve
Practice Problem 2
Calculate the enthalpy change
associated with converting 1.00 mol
of ice at –25.0 ºC to water vapor at
125 ºC and 1 atm pressure.
c(ice) = 2.09 J / g °C
c(liquid) = 4.18
c(steam) = 1.84
DH(fus) = 6.01 kJ/mol
DH(vap) = 40.7 kJ/mol
Phase Diagrams
What’s on the test?
 Multiple choice (~20 points)
 Ordering (~15 points)
 Free response (~65 points)
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Heating curve calculations
Phase diagram interpretations
Clausius Clapeyron manipulations
Unit cell calculations
Short answer questions