Tuesday, January 25, 2011

This morning, we walked into class and Mr. Henderson passed out our semester grade reports. Once he was sure that everyone had received their grades, he asked us to turn to page 31 in our Thermochemistry unit packets. He gave us the answers for last night's WebAssign:
1. False
2. B
3 D
4. C
5. B
6. D
7. A
8. B
9. D
10. True
11. A, B, C
12. D, A, C, B
13. A
14. A

Subsequently, Mr. H told us to get out our lab notebooks while we looked at Daria's blog. As he read through it, he explained to us what was happening at the molecular level during state changes of water. First, the particles in the solid crystal lattice begin to vibrate when thermal energy (heat) is added (temperature increase). They wiggle more and more violently until they turn into a puddle (liquid). The fluid particles have small intermolecular forces and are relatively close together. When heat is added, they begin to vibrate and move about the puddle until so much kinetic energy is gained that the molecules "pop" out of the puddle and "fly" (as Matt said) because they are now a gas. Particles in a gas are far apart and if one were to walk through gas, there would be no resistance. Particles in a liquid are semi-close to each other and if one were to walk through liquid, there would be slight resistance. However, particles in a solid are very close together and if one were to walk through a solid...they wouldn't! Mr. H reminded us: "You can never walk through a solid."

We then turned to our TC9 lab in our notebooks. Mr. Henderson told us that we must tape our data table and graphs into the lab. We also must write a conclusion/discussion, answering all 4 questions required in a fluid manner

1. Observe the plateaus on the two graphs. What could be happening during these plateaus?

2. Determine the melting point and freezing point of lauric acid. How do they compare?

3. Describe what happens at the particle level as heat is added to the substance and its temperature increases.

4. Describe what happens at the particle level as heat is added to a substance and its phase changes.

Henderson instructed us to take some notes:

• A plateau does not equal [Delta] T
• Melting point and freezing point are the same temperature! For lauric acid, it's 44 degrees Celsius
• Plateau = mix of solid/liquid or liquid/gas

After discussing this, Mr. H gave us 5 minutes to work on the conclusion. Then, he said that there would be a demo in the back of the class later on involving boiling water and capturing the emitted gas.

Even more after, we turned to page 13 in our Thermochemistry packets. First, we did numbers 1-13:

1. D E F

2. A

3. F

4. NONE

5. A

6. D

7. D E F

8. E

[oops, where's the 9?]

10. B

11. E

12. C

13. D

The bottom of page 13 is as Mr. Henderson said "basically lab TC9" except with water. The labels for the diagram are: 1 - solid, 2 - solid/liquid (0 degrees), 3 - liquid, 4 - liquid/gas (100 degrees), 5- gas. Then, we turned to the next page (14) where we completed questions 15-28:

15. 2, 4

16. 4

17. 1

18. 2

19. 2

20. 2

21. 4

22. 5

23. 2

24. 3

25. 4

26. 1, 3, 5

27. 2

28. 4

We migrated to the back of the room to finish the demo. Mr. H connected a thin copper pipe to the flask with the boiling water. We observed as steam spewed from the end. We thought this was gas. NO! It was water!!!!!!! As the gas traveled through the pipe, it cooled back to liquid state. Mr. H then put the burner under the pipe. He showed us that this was real gas. It was SO hot that he could light a match! Then he placed a paper at the end, which he burned "I'M HOT" into. Then the bell rang.

Homework: WebAssign Due Thursday the 27th, page 15 in packet