1. Vapor Pressure
Vaporization - change from liquid to gas at boiling point.
Evaporation - change from liquid to gas below boiling point
Heat (or Enthalpy) of Vaporization (DHvap )- the energy required to vaporize 1 mol at 1 atm.

2. Vaporization is an endothermic process - it requires heat.
Energy is required to overcome intermolecular forces.
Responsible for cool earth.
Why we sweat. (Never let them see you.)

3. Condensation Change from gas to liquid.
Achieves a dynamic equilibrium with vaporization in a closed system.
What is a closed system?
A closed system means matter can’t go in or out.
Put a cork in it.
What the heck is a “dynamic equilibrium?”

4. Dynamic equilibrium
When first sealed the molecules gradually escape the surface of the liquid.

5. Dynamic equilibrium
When first sealed the molecules gradually escape the surface of the liquid.
As the molecules build up above the liquid some condense back to a liquid.

6. Dynamic equilibrium
When first sealed the molecules gradually escape the surface of the liquid.
As the molecules build up above the liquid some condense back to a liquid.
As time goes by the rate of vaporization remains constant but the rate of condensation increases because there are more molecules to condense.

7. Dynamic equilibrium
When first sealed the molecules gradually escape the surface of the liquid
As the molecules build up above the liquid some condense back to a liquid.
As time goes by the rate of vaporization remains constant but the rate of condensation increases because there are more molecules to condense.
Equilibrium is reached when

8. Dynamic equilibrium Rate of Vaporization = Rate of Condensation
Molecules are constantly changing phase “Dynamic”
The total amount of liquid and vapor remains constant “Equilibrium”

9. Vapor pressure The pressure above the liquid at equilibrium.
Liquids with high vapor pressures evaporate easily. They are called volatile.
Decreases with increasing intermolecular forces.
Bigger molecules (bigger LDF)
More polar molecules (dipole-dipole)

10. Vapor pressure Increases with increasing temperature.
Easily measured in a barometer.

11. Dish of Hg
Vacuum
Patm=
760 torr
A barometer will hold a column of mercury 760 mm high at one atm

12. Dish of Hg
Vacuum
Patm=
760 torr
A barometer will hold a column of mercury 760 mm high at one atm.
If we inject a volatile liquid in the barometer it will rise to the top of the mercury.

13. Water
A barometer will hold a column of mercury 760 mm high at one atm.
If we inject a volatile liquid in the barometer it will rise to the top of the mercury.
There it will vaporize and push the column of mercury down.
Patm=
760 torr
Dish of Hg

14. Dish of Hg The mercury is pushed down by the vapor pressure.
Water Vapor
The mercury is pushed down by the vapor pressure.
Patm = PHg + Pvap
Patm - PHg = Pvap
= 24 torr
736 mm Hg
Dish of Hg

15. Temperature Effect Energy needed to overcome intermolecular forces
# of molecules
Kinetic energy

16. Energy needed to overcome intermolecular forces
At higher temperature more molecules have enough energy - higher vapor pressure.
Energy needed to overcome intermolecular forces
Energy needed to overcome intermolecular forces T1 T1
# of molecules T2
Kinetic energy

17. Changes of state
The graph of temperature versus heat applied is called a heating curve.
The temperature a solid turns to a liquid is the melting point.
The energy required to accomplish this change is called the Heat (or Enthalpy) of Fusion DHfus

18. Water and Steam Water and Ice
Heating Curve for Water
Steam
Water and Steam
Water
Water and Ice
Ice

19. Heat of Vaporization Heat of Fusion
Heating Curve for Water
Slope is Heat Capacity
Heat of
Vaporization
Heat of
Fusion

20. Melting Point
Melting point is determined by the vapor pressure of the solid and the liquid.
At the melting point the vapor pressure of the solid = vapor pressure of the liquid

21. Solid Water
Liquid Water
Water Vapor Vapor

22. Water Vapor Vapor Solid Water Liquid Water
If the vapor pressure of the solid is higher than that of the liquid the solid will release molecules to achieve equilibrium.
Solid Water
Liquid Water
Water Vapor Vapor

23. While the molecules of condense to a liquid.
Solid Water
Liquid Water
Water Vapor Vapor

24. This can only happen if the temperature is above the freezing point since solid is turning to liquid.
Solid Water
Liquid Water
Water Vapor Vapor

25. Water Vapor Vapor Solid Water Liquid Water
If the vapor pressure of the liquid is higher than that of the solid, the liquid will release molecules to achieve equilibrium.
Solid Water
Liquid Water
Water Vapor Vapor

26. While the molecules condense to a solid.
Solid Water
Liquid Water
Water Vapor Vapor

27. The temperature must be above the freezing point since the liquid is turning to a solid.
Solid Water
Liquid Water
Water Vapor Vapor

28. Water Vapor Vapor Solid Water Liquid Water
If the vapor pressure of the solid and liquid are equal, the solid and liquid are vaporizing and condensing at the same rate. The Melting point.
Solid Water
Liquid Water
Water Vapor Vapor

29. Boiling Point
Reached when the vapor pressure equals the external pressure.
Normal boiling point is the boiling point at 1 atm pressure.
Super heating - Heating above the boiling point.
Supercooling - Cooling below the freezing point.

30. Phase Diagrams.
A plot of temperature versus pressure for a closed system, with lines to indicate where there is a phase change.

31. Solid
Liquid
Gas D D
Pressure D C
1 Atm B D A
Temperature

32. Solid
Liquid
Gas
Critical Point
Pressure
Triple Point
Temperature

33. This is the phase diagram for water.
Solid
Liquid
Gas
This is the phase diagram for water.
The density of liquid water is higher than solid water.
Pressure
Temperature

34. Pressure 1 Atm Temperature This is the phase diagram for CO2
The solid is more dense than the liquid
The solid sublimes at 1 atm.
Pressure
Liquid
Solid
1 Atm
Gas
Temperature