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Announcements. 1 st HW answer key available Friday afternoon LTEF poster due by 4:00 pm 10/1 2 nd 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?.

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**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**• Different liquids have different vapor pressures. Why? • How does temperature affect vapor 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 As T increases, vapor pressure increases What happens when T gets 100ºC? Boiling point: T at which the vapor pressure equals atm pressure. Temperature vs. Vapor Pressure**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.**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**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

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