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. Discuss rates of evaporation and condensation on board.

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, vapor pressure increases What happens when T gets 100ºC? Boiling point: T at which the vapor pressure equals atm pressure. For H2O: T (ºC) P(torr) 0.0 4.58 25.0 23.76 40.0 55.32 70.0 233.7 90.0 525.8

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 DH(fus) = 6.01 kJ/mol c(liquid) = 4.18 DH(vap) = 40.7 kJ/mol c(steam) = 1.84

Phase Diagrams

What’s on the test? Multiple choice (~20 points) Ordering (~15 points) Free response (~65 points) Heating curve calculations Phase diagram interpretations Clausius Clapeyron manipulations Unit cell calculations Short answer questions