1. Liquids and Solids
Changes of State

2. Objectives Identify changes of state
Define Equilbrium and 2Le Chatelier’s Principle.
Predict changes in equilibrium using Le Chatelier’s Principle.

3. Equilibrium
Equilibrium – a dynamic state in which two opposing changes occur at equal rates in a closed system. Changes of State solid  liquid melting solid  gas sublimation liquid  solid freezing liquid  gas vaporization gas  liquid condensation gas  solid deposition

5. An Equilibrium Equation
Evaporation of a liquid
Liquid + energy  vapor
Condensation of a liquid
Vapor  liquid + energy
Liquid-vapor equilibrium
liquid + energy vapor

6. Le Chatelier’s Principle
A system at equilibrium will shift to offset a stress or change in conditions imposed on the system.

7. Equilibrium and Temperature
liquid + energy vapor
Change
Shift in Equilibrium
Increase in temperature
forward
Decrease in temperature
reverse

8. Equilibrium and Concentration
liquid + energy vapor
Change
Shift in Equilbrium
Addition of liquid
Removal of liquid
Addition of vapor
Removal of vapor
Decrease in container volume
Increase in container volume

9. Equilibrium Vapor Pressure
Pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature
-an increase in temperature causes an increase in equilibrium vapor pressure; result of increased K.E. of the liquid particles.

12. Volatile and Non-volatile liquids
Volatile Liquid – a liquid that readily evaporates at room temp.; liquids with low intermolecular forces.

13. Boiling
Boiling…
…occurs when the equilibrium vapor pressure of a liquid equals the atmospheric pressure
…conversion of a liquid to a vapor within the liquid as well as at the surface.
Normal Boiling Point: boiling point at standard atmospheric pressure (100oC for water)

14. Boiling

15. Energy and Boiling

16. Molar Heat of Vaporization
The amount of energy needed to vaporize 1 mole of a liquid at its boiling point

17. Freezing and Melting Freezing: Liquid  solid + heat energy Melting:
Solid + heat energy  liquid
Normal freezing point: temperature at which a solid and liquid are at equilbrium at standard pressure (0oC for water
Molar Heat of Fusion – energy required to melt one mole of a solid at its melting point.

19. Phase Diagram
Triple Point – temperature and pressure conditions at which the solid, liquid, and gas phases of a substance can coexist at equilibrium Critical temperature - temperature above which a substance cannot exist in the liquid phase. Critical pressure – the lowest pressure at which a substance can exist as a liquid at the critical temperature.