2. Behavior of a Liquid in a Closed Container a) Initially b) at Equilibrium
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3. The Rates of Condensation and Evaporation
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4. Vapor Pressure Pressure of the vapor present at equilibrium.
The system is at equilibrium when no net change occurs in the amount of liquid or vapor because the two opposite processes exactly balance each other.
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5. What is the vapor pressure of water at 100°C? How do you know?
The vapor pressure of water at 100oC is 1 atm. You know this because atmospheric pressure is 1 atm and this is the temperature at which we observe water to boil.
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6. Vapor Pressure
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7. Vapor Pressure
Liquids in which the intermolecular forces are large have relatively low vapor pressures.
Vapor pressure increases significantly with temperature.
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8. Vapor Pressure vs. Temperature
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9. Clausius–Clapeyron Equation
Pvap = vapor pressure ΔHvap = enthalpy of vaporization R = J/K·mol T = temperature (in kelvin)
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10. The vapor pressure of water at 25°C is 23
The vapor pressure of water at 25°C is 23.8 torr, and the heat of vaporization of water at 25°C is 43.9 kJ/mol. Calculate the vapor pressure of water at 65°C.
ln(23.8 torr/Pvap,T2) = [(43900 J/mol)/( J/K·mol)][(1/338 K) – (1/298)]
Pvap,T2 = 194 torr
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11. Changes of State To play movie you must be in Slide Show Mode
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12. Heating Curve for Water
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13. CONCEPT CHECK!
Which would you predict should be larger for a given substance: ΔHvap or ΔHfus? Explain why.
ΔHvap should be larger because it will take a lot more energy to break the intermolecular forces between the liquid molecules to completely break apart to form a gas.
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14. Phase equilibrium lines
A convenient way of representing the phases of a substance as a function of temperature and pressure:
Triple point
Critical point
Phase equilibrium lines
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15. Phase Diagram for Carbon Dioxide
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16. Phase Diagram for Water
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17. CONCEPT CHECK!
As intermolecular forces increase, what happens to each of the following? Why?
Boiling point
Viscosity
Surface tension
Enthalpy of fusion
Freezing point
Vapor pressure
Heat of vaporization
Boiling point increases
Viscosity increases
Surface tension increases
Enthalpy of fusion increases
Freezing point increases
Vapor pressure decreases
Heat of vaporization increases