1. Unit 4: Energy of Phase Changes

2. Bell Ringer
What are the three phases (states) of matter?

3. Kinetic Molecular Theory of Matter
Particles of matter are always in motion.
The kinetic energy (speed) of these particles increases as temperature ncreases.

4. Add Heat Add Heat Remove Heat Remove Heat
Q: What physical arrangement of the molecules of water could describe the differences in the states of matter seen below?
Remove Heat
Remove Heat
Solid
Liquid
Gas
Molecules held tightly together
but can still vibrate
Has definite shape
Molecules vibrate more rapidly
enough to overcome the forces
that hold them together
Can slide past one another
Has the shape of container
Molecules have overcome the forces that keep them near their neighbors in a liquid and they fly apart
Add Heat
Add Heat

5. Solid Liquid Gas Tightly Vibrating Molecules
Has definite shape
Molecules vibrate more rapidly
Can slide past one another
Very Rapid Vibrations
they fly apart

6. Heating vs. Cooling Heating Cooling
Increases the vibration of the molecules
Cooling
Slows down the motion of the molecules

7. How does a Thermometer work?
Red Tip
Reservoir of colored alcohol
with really thin glass walls.
When molecules surrounding the thermometer strike the bulb.....
They transfer some of their energy to the alcohol inside
Alcohol expands
Height of liquid
can be used to measure the “hotness” of the surroundings

8. “Cold” Surrounds??
What happens when the thermometer is placed in surroundings that are “colder” than the alcohol in the reservoir?
Energy flows from the hotter alcohol to the surroundings
Molecules in the alcohol slow down
Level of the alcohol falls

9. How to read a thermometer “hotness meter”……
Temperature
A measure of the “hotness” of a substance or how fast the molecules are moving.
3 Temperature Scales
Celsius
Most Common: Water boils at 100° C, freezes at 0° C
Fahrenheit
Mostly in the U.S.: Water boils at 212° F, freezes at 32° F
Kelvin
More scientific: Absolute zero is 0 K

11. Temperature vs. Heat Temperature Heat
A measure of the “hotness” of a substance or how fast the molecules are moving.
Heat
A measure of the energy transferred into or out of a system.
Always flows from hot  cold

12. Consider the following situation….
Metal plate and a wooden dish left in the refrigerator over night are now placed on the counter.
Which would feel colder?
Metal plate because it transfers energy more rapidly from our fingers than wood
VS.

13. Consider the following situation….
If you wanted to warm up the water in your wading pool, would it be better to use a teacup full of water at 100° C or a bucket full of water at 50° C?
VS.
(4 mins 51 seconds)

14. Consider the following situation….
If you wanted to warm up the water in your wading pool, would it be better to use a teacup full of water at 100° C or a bucket full of water at 50° C?
VS.
(4 mins 51 seconds)

15. Thermal Expansion of a Gas
If you blow up a balloon and place it in the sun, what will happen to it? WHY??

16. Work on WS #1 & WS #2

17. Bell Ringer
Describe in steps how a thermometer works when placed in a hot water bath…
If an ice cube is placed in a hot cup of soup, describe the energy transfer and the motion of the molecules.

18. Go over WS #1 & WS #2

19. WS #1: Problem #2
Suppose someone in your class said that when water freezes, it is because the molecules get cold and turn hard. Provide a better explanation for this in terms of the motion of molecules and the attractions between them.

20. WS #1: Problem #3
When asked, "What is between the molecules in liquid water?", a student replied that water filled in the spaces. Is this answer correct? Explain.

21. WS #2: Problem #1
You decide to boil water to cook noodles. You place the pan of water on the stove and turn on the burner.
How does the behavior of the water molecules change as the pan of water is heated?
What about your answer to (a) would change if there were more water in the pan?

22. WS #2: Problem # 2
What property of matter best describes the way a typical alcohol thermometer works? Explain (in terms of energy transfer) why the alcohol level in the thermometer rises (or falls) when you place the thermometer in contact with both warmer (or colder) objects.

23. WS #2: Problem #3
If you feel feverish, why can't you take your own temperature with your hand?

24. WS #2: Problem #4
Your older brother announces that the lid to a jar of pickles from the refrigerator is “impossible” to loosen. You take the jar, hold the lid under the hot water from your sink’s faucet for a few seconds, and calmly open the jar. Your brother, when faced with this blow to his pride, claims that he loosened it for you. What knowledge of materials have you applied in this situation that really explains how you were able to open the lid?

26. Phase Changes Sublimation: solid  gas. Deposition: gas → solid.
Vaporization/Evaporation: liquid  gas.
Condensation: gas → liquid.
Melting (Fusion): solid  liquid.
Freezing: liquid  solid.

27. Phase Diagrams
Show the phases of a substance at different temperatures and pressures.
Triple point: temperature and pressure at which all three phases are in equilibrium.
Critical point: above this point, you cannot distinguish between liquids and gases

28. Melting/Freezing Point Lab

29. Heating and Cooling Curves

30. Bell Ringer
What process occurs when we add heat energy to a solid and it turns into a liquid?
Describe what happens to the molecules of a solid when we add heat energy.
What is the melting point of water?
In Celsius?
In Fahrenheit?

31. Review
What happens to molecules as the temperature increases? What are on the axis of a phase change diagram? What are the three phases that a substance passes through? Do all phase change diagrams look the same, why?

32. What is a plateau?
A high, flat area of land where the elevation doesn’t change

33. What does a plateau mean on a heating curve?
During the Plateau for Melting:
While the energy of the contents of the beaker was continually increasing….
the temperature (or “hotness”) of the solid-liquid mixture was relatively constant
KE used to separate molecules, PE is being stored
Once the beaker contained only liquid:
The temperature rose steadily.
The molecules are free to move around more rapidly.

34. Heating Curve
The purpose of a heating curve is to see the temperature change as heat (energy) is added to a system.
From a heating curve you can get a substances melting/freezing point and boiling point

35. Heating Curve As heat is added to the solid the temperature increases.
When it reaches the melting point the temperature remains constant until all of the solid has become liquid.
Temperature is constant

36. Heating Curve
Once the substance has all become liquid the temperature will begin to rise again.
The temperature rises until it reaches the boiling point.
Again, the temperature will remain constant until all of the liquid has become vapor/gas

37. Heating Curve Gas - KE  Boiling - PE  Liquid - KE  Melting - PE 
Solid - KE 

38. What does a plateau mean on a cooling curve?
During the Plateau for Freezing:
While the energy of the contents of the beaker was continually decreasing….
the temperature (or “hotness”) of the solid-liquid mixture was relatively constant
PE Stored is “squeezed out” as thermal energy
Keeps substance at a constant temp
Once the beaker contained only solid:
The temperature decreased steadily.
The molecules are slowing down

39. Cooling Curve
Cooling curve is the same thing as a heating curve, just in the opposite direction. In this graph we start at high temperatures and get lower. Remember that melting point occurs at the same temperature as freezing point.

40. Freezing and Melting “TOP 5”
1. MELTING: A substance melts by changing from a solid to a liquid
FREEZING: A substance freezes by changing from a liquid to a solid.
2. Substances freeze at the SAME temperature that they melt.
3. The amount doesn’t make a difference –
subs. will melt or freeze at the same temp.
4. A plateau is a flat section on a graph where the temps. stay the same and the substance is changing phase.
5. Heat Energy is either absorbed or released during a phase change.

41. Bell Ringer Is this a heating or cooling graph?
During what time/stage did the substance freeze?
Label what stage was it a Liquid? Solid? Both?