topic: liquids & vapor pressure do now: compare i 2 and f 2 why is f 2 a gas at room temp. and i...
TRANSCRIPT
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 systemopen system Evaporation continues until all liquid is gone Fig b: closed systemclosed system Rate of evaporation = rate of condensation System appears static due to equilibrium
molecules in liquid phase have range of KE; some have enough KE to “escapeescape” from liquid phase
How does evaporation occur?
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 PointNormal Boiling Point:
temp at which VP liquid = 1 atm
• Substances with high bp’s have strong IMF’s
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
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
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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• Weak• Strong• Weak• Strong