1. Chapter 23: Change of Phase

2. Matter exists in 3 main phases
Phase to Phase
Matter exists in 3 main phases
Solid
Liquid
Gas
State of matter dependent upon temperature and pressure (involve a transfer of energy)

3. Evaporation Evaporation is Phase change from liquid to gas
Takes place at the surface of the liquid (hot particles leave; cool ones are left behind)
A cooling process
How do you cool your body?
How do you stay cool at Six Flags?
How do you cool a hot cup of coffee?
Eureka Video – Evaporation & Condensation
Tennisball activity – give all tennisballs, some colored. When colored ones reach ‘surface’ – front row – they get throw to me – notice how the temperature drops and the total number of particles drops

4. Condensation is Condensation Phase change from gas to liquid
loss of energy due to collision
loss of energy due to attractive forces
A warming process
Why do you feel extra warm on a muggy day?

5. Condensation and Evaporation are constantly taking place
The Going Rate
Condensation and Evaporation are constantly taking place
Condensation and Evaporation occur together.
A hot cup of coffee cools by evaporation, the surrounding air warms

6. Evaporation>Condensation-cooling
The Going Rate
Evaporation and Condensation take place at the same time
Evaporation>Condensation-cooling
Evaporation<Condensation-warming
Evaporation=Condensation-equilibrium

7. The Going Rate
What can you conclude about a dish of water on a table for several days that has no change in the water level?
Why do you feel chilly after emerging from a shower?
Why do you not feel as chilly if you stay in the shower to dry off?

8. There’s Something in the Air
Saturation of air must occur for condensation to be present
When slow moving molecules collide, they stick together (at higher speeds, they can bounce apart)
Cloud formation attributed to condensation
warm air rises = expands = cools = molecules stick together = condensation upon molecules/ions
Fog - a cloud that forms near the ground

9. It’s Time to Chill Out Freezing Freezing temperature can be altered
Change from a liquid to a solid state
Freezing temperature can be altered
Change in pressure
Adding salt or sugar

10. You’re Getting Warmer Boiling Changing from liquid to gas
Occurs beneath the surface
Cooling process - molecules having the highest KE escape

11. Dependent on temperature and pressure
Boiling
Dependent on temperature and pressure
Pressure of vapor within the bubbles > pressure of surrounding liquid
Temperatures below boiling point, vapor pressure is not great enough

12. Boiling Higher Atmospheric Pressure Increases Boiling Point
molecules are required to move faster to exert increased pressure within the bubble

13. Lower Pressure (high altitudes), Decreases boiling point
Pressure Cooker
Vapor builds up inside sealed cooker
Pressure on the surface is increased
Raises boiling point
Increased Temp. cooks the food

14. Boiling and Freezing can occur at the same time Regelation
2 Phases for the price of 1
Boiling and Freezing can occur at the same time
Regelation
Melting takes place under pressure
Freezing occurs when pressure is reduced

15. Let’s Energize Energy is needed to go from solid to liquid to gas
Energy is released when going from gas to liquid to solid

16. Change of Phase a d b c a

17. Changes of Phase Ice (A) Energy goes to K.E. + P.E.
Steeper Line = easier to heat up; less goes to P.E.

18. Changes of Phase Melting (B) Energy goes to P.E. No temperature change
80 calories of heat must be absorbed to melt 1 gram
The temperature rises once all the ice melts

19. Changes of Phase Liquid Water (C) Energy goes to K.E. + P.E.
Each additional calorie raises the temp. by 1 degree Celsius until it reaches boiling

20. Changes of Phase Vaporizing (D) Energy goes to P.E. No Temp. change
540 calories of heat must be absorbed to vaporize 1 gram

21. Changes of Phase Check Question
How much energy is released when a gram of steam at 100ºC condenses to water at 100ºC ?
How much energy is released when a gram of steam at 100ºC condenses then cools to ice water at 0ºC ?

22. Changes of Phase Final Question
How much energy is released when you cool 20 grams of 105°C steam into -10°C ice?