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Chapter 12.3 : Changes of State

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Chapter 12.3 : Changes of State

1. 1. Changes Of state<br />Chapter 12.3<br />Objectives:<br />Explain the relationship between equilibrium and changes of state.<br />Predict changes in equilibrium using Le Chatelier’s principle.<br />Explain what is meant by equilibrium vapor pressure.<br />Describe the processes of boiling, freezing, melting, and sublimation.<br />Interpret phase diagrams.<br />
2. 2. Equilibrium<br />Defined as: a dynamic condition in which two opposing changes occur at equal rates in a closed system.<br />Closed system: matter cannot enter or leave, but energy can<br />Analogy:<br />Public swimming pool<br />Morning: more people entering than leaving<br />Afternoon: number of people entering and leaving are the same<br />This would be equilibrium<br />
3. 3. Equilibrium and Changes of State<br />Evaporation of water in a closed container<br />Vacuum over liquid<br />Same temperature as surroundings ( 25oC)<br />Water and container are the system<br />**Single Phase Liquid<br />**Evaporation begins at constant rate<br />**Rate of evaporation is equal to rate of condensation<br />**Some condensation occurs<br />Equilibrium<br />
4. 4. Possible Phase Changes<br />Change of State Process Example<br />Solid Liquid melting candle<br />Solid Gas sublimation Rock show<br />Liquid Solid freezing Lake freezing<br />Liquid Gas vaporization puddle<br />Gas Liquid condensation bathroom<br />Gas Solid deposition Frost <br />
5. 5. An Equilibrium Equation<br />liquid + heat energy vapor<br />vapor liquid + heat energy <br />liquid + heat energy vapor<br />Reversible: vapor is being formed at the same RATE as liquid.<br />
6. 6. Le Chatelier’s Principle<br />When a system at equilibrium is disturbed by application of a stress, it attains a new equilibrium position that minimizes the stress.<br />Stress:<br /><ul><li>Change in</li></ul>Concentration<br />Pressure<br />temperature<br />These will cause a shift in equilibrium<br /><ul><li> Will always adjust to move back to equilibrium</li></ul>liquid + heat energy vapor<br />Example: <br />1. add liquid (increase concentration)<br />2. Start to create more vapor<br />3. Shift to the right<br />
7. 7. Shifts in Equilibrium<br />liquid + heat energy vapor<br />Change Shift _<br />Add liquid Right<br />Remove liquid Left<br />Add Vapor Left<br />Remove Vapor Right<br />Decrease Container Volume Left<br />Increase Container Volume Right<br />Decrease in Temperature Left<br />Increase in Temperature Right<br />
8. 8. Equilibrium Vapor Pressure of a Liquid<br />Defined as: the pressure exerted by a vapor in equilibrium with its corresponding liquid at a given temperature<br />
9. 9. Volatile and Nonvolatile Liquids<br />Volatile Liquids: <br />Liquids that evaporate readily<br />Weak attractive forces<br />Nonvolatile <br />Does not evaporate readily<br />Stronger attractive forces<br />Equilibrium vapor pressure<br />Depends on <br />Nature of liquid<br />Temperature<br />
10. 10. Boiling<br />Conversion of a liquid to a vapor within the liquid to a vapor within the liquid as well as at its surface.<br />Occurs when <br />Equilibrium vapor pressure = atmospheric pressure<br />Boiling Point<br />Temperature at which the equilibrium vapor pressure of the liquid equals the atmospheric pressure<br />High elevations<br />Lower atmospheric pressure<br />Water boils at lower temperatures<br />Food takes longer to cook<br />
11. 11. Molar Heat of Vaporization<br />The amount of heat energy needed to vaporize one mole of liquid at its boiling point.<br />100.0<br />Temperature(oC)<br />0.0<br />Heat of vaporization<br />Heat added (KJ)<br />
12. 12. Freezing and Melting<br />Freezing point<br />Temperature at which the solid and liquid are in equilibrium at 1 atm pressure.<br />Melting is the reverse of freezing.<br />liquid solid + heat energy<br />solid + heat energy liquid <br />solid + heat energy liquid<br />
13. 13. Molar Heat of Fusion<br />The amount of heat energy required to melt one mole of solid at its melting point.<br />100.0<br />Temperature(oC)<br />0.0<br />Heat added (KJ)<br />Heat of fusion<br />
14. 14. Sublimation and Deposition<br />Sublimation<br />Change of state from a solid directly to a gas<br />Deposition<br />Change of state from a gas directly to a solid<br />solid + heat energy vapor<br />
15. 15. Phase Diagrams<br />Graph of pressure versus temperature that shows the conditions under which the phases of a substance exist.<br /><ul><li> Triple Point
16. 16. indicates the temperature and pressure conditions at which the solid, liquid, and vapor of a substance can coexist at equilibrium.
17. 17. Critical point
18. 18. indicates the critical temperature and critical pressure.
19. 19. Critical temperature
20. 20. temp. above which substance cannot exist as a liquid.
21. 21. Critical pressure
22. 22. lowest pressure at which the substance can exist as a liquid at the critical temperature.</li>