PHASE CHANGES

VAPOR PRESSURE

 

PHASE CHANGES

ADD HEAT TO A SOLID

    SOLID MELTS AND BECOMES LIQUID

    EVENTUALLY LIQUID BECOMES GAS

THREE PHASES

    SOLID

    LIQUID

    GAS

FOUR PROCESSES

    MELTING

    EVAPORATION OR VAPORIZATION

    CONDENSATION

    FREEZING

MORE THAN ONE PROCESS CAN OCCUR AT ONE TIME

    OUTCOME IS A FUNCTION OF RATES!

      IF RATEEVAPORATION > RATECONDENSATION

        EVENTUALLY ALL THE LIQUID EVAPORATES

      IF RATECONDENSATION > RATEEVAPORATION

        EVENTUALLY ALL THE GAS CONDENSES

      IF RATEEVAPORATION = RATECONDENSATION

        THERE IS NO NET CHANGE EVEN THOUGH BOTH PROCESSES ARE, IN FACT, OCCURRING AT THE SAME TIME!

 

ANY PROCESS IN WHICH

    RATEFORWARD = RATEREVERSE

    IS A STATE OF DYNAMIC EQUILIBRIUM

 

MOLECULES ENTERING THE VAPOR STATE EXERT A PRESSURE

IF SYSTEM IS AT EQUILIBRIUM, IT IS THE "EQUILIBRIUM VAPOR PRESSURE"

    THE EQUILIBRIUM VAPOR PRESSURE IS THE PRESSURE OF THE VAPOR IN EQUILIBRIUM WITH THE LIQUID

MEASUREMENT OF THE VAPOR PRESSURE OF WATER AND ETHYL ALCOHOL

IF YOU INCREASE THE TEMPERATURE 10o

    RATEEVAPORATION INCREASES

    RATECONDENSATION DECREASES

    EVENTUALLY REESTABLISHES A NEW EQUILIBRIUM WITH A HIGHER VAPOR PRESSURE

 

BOILING POINT

TEMPERATURE AT WHICH THE VAPOR PRESURE EQUALS THE APPLIED PRESSURE

    NORMAL BOILING POINT IS THE TEMPERATURE AT WHICH VAPOR PRESSURE EQUALS 1 ATMOSPHERE

 

MELTING POINT

TEMPERATURE AT WHICH THE SOLID AND LIQUID PHASE ARE IN EQUILIBRIUM

 

ENERGY REQUIREMENTS

MOLAR HEAT OF FUSION (DHfus)

    ENERGY (KILOJOULES) REQUIRED TO MELT ONE MOLE OF SOLID

MOLAR HEAT OF VAPORIZATION (DHvap)

    ENERGY (KILOJOULES) REQUIRED TO VAPORIZE ONE MOLE OF LIQUID

HEATS OF VAPORIZATION AND BOILING POINTS
SUBSTANCE BOILING POINT DHvap (kJ/mol)
ARGON (Ar) -186 6.3
METHANE (CH4) -164 9.2
ETHYL ETHER 34.6 26.0
ETHANOL 78.3 39.3
WATER 100 40.79
MERCURY 357 59.0

MOLAR HEAT OF SUBLIMATION (DHsub)

    ENERGY (KILOJOULES) REQUIRED TO VAPORIZE (SUBLIME) ONE MOLE OF SOLID

SPECIFIC HEAT

    ENERGY (JOULES) REQUIRED TO RAISE THE TEMPERATURE OF ONE GRAM OF THE SUBSTANCE BY ONE DEGREE CELSIUS

      DIFFERENT FOR SOLID, LIQUID, AND GAS

 
SPECIFIC HEATS OF H2O
PHASE SPECIFIC HEAT (J/go)
ICE (SOLID) 2.09
WATER (LIQUID) 4.18
STEAM (GAS) 2.02
 

HEATING AND COOLING CURVES

HEATING CURVE

COOLING CURVE

 

PHASE DIAGRAMS

CARBON DIOXIDE

    AT THE TRIPLE POINT, 5.2 ATM AND -57o, ALL THREE PHASES EXIST IN EQUILIBRIUM

      CANNOT HAVE LIQUID BELOW THE TRIPLE POINT

      CANNOT HAVE LIQUID CARBON DIOXIDE AT 1 ATM

      SOLID CARBON DIOXIDE SUBLIMES AT 1 ATM

    ABOVE THE CRITICAL POINT ONLY THE GAS PHASE EXISTS

    MOST SUBSTANCES HAVE A PHASE DIAGRAM WITH A SIMILAR SHAPE

BUT NOT WATER

    NOTE THAT AS THE PRESSURE GOES UP, THE MELTING POINT GOES DOWN

      RESPONSIBLE FOR ICE SKATING

 

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