Click here and go over slides from Wisc-Online before talking notes! Topic: Liquids & Vapor Pressure Do Now: Compare I2 and F2 Why is F2 a gas at room temp. and I2 a solid Click here and go over slides from Wisc-Online before talking notes!

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

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

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

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

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

all liquids: as T ↑ the VP ↑ Boiling Point

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

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

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

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

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