1. Topic: Liquids & Vapor Pressure Do Now: Compare I 2 and F 2 Why is F 2 a gas at room temp. and I 2 a solid Click here and go over slides from Wisc-Online before talking notes!

2. Vapor Vapor is the gas phase of substance that is normally liquid at room temperature Some evaporation occurs at all temperatures (like you saw with the ice cube) The easier a substance evaporates, the weaker the IMF

3. open system Fig a: open system Evaporation continues until all liquid is gone closed system Fig b: closed system Rate of evaporation = rate of condensation System appears static due to equilibrium

4. molecules in liquid phase have range of KE; escape some have enough KE to “escape” from liquid phase How does evaporation occur?

5. Vapor Pressure –Pressure exerted by vapor over its liquid –VP is affected by temperature: higher the T, higher the VP

6. Vapor Pressure VP does NOT depend on how much liquid is present VP depends only on temperature

7. all liquids: as T ↑ the VP ↑ Boiling Point

8. Temperature at which: VP liquid = external atmospheric P Normal Boiling PointNormal Boiling Point: temp at which VP liquid = 1 atm Substances with high bp’s have strong IMF’s

10. Boiling vs. Evaporation BOILING occurs throughout liquid occurs at definite T occurs at constant T only spontaneous when VP = external pressure EVAPORATION occurs at surface of liquid (or solid) occurs at all T liquid cools off as evaporates spontaneous all the time

11. Boiling and Pressure If increase external pressure (ex: camping in Death Valley), boiling point is ____ than 100 o C If decrease external pressure (ex: eating Raman noodles at top of Mt. Whitney), the boiling point is ____ than 100 o C > <

12. IMF in Liquids WEAK FORCES High VP High rate evaporation Low bp STRONG FORCES Low VP Low rate evaporation High bp

13. Strong or Weak attractive forces? High vapor pressure High boiling point Low boiling point Low vapor pressure Evaporates rapidly Evaporates slowly Weak Strong Weak Strong Weak Strong