p>Introduction
Objectives
? Investigate an aspect of entropy.
? Apply an understanding of entropy to a system.
Purpose:
(a) Materials
The following materials were used in the laboratory experiment
• Rubber band
• Ruler
• One gallon milk or water jug
• Tap water
• Door handle
• Ice
• Blow dryer
(b)Procedures
1. Cut the rubber band so that you have a rubber strip instead of a rubber band.
2. Fill the jug half-full of tap water.
3. Tie one end of the rubber band to the jug, and the other end to a sturdy door handle or other device you can use to “hang” the jug from.
4. Make an initial measurement as a reference point for the position of the jug in terms of its distance from the door handle. In other words, you want to know how long the rubber band allows the half-full jug of water to hang from the door handle.
Predict what will happen if the rubber band is heated (will it get longer or shorter?) and if the rubber band is cooled. Now you will perform this experiment:
5. Take two (2) ice cubes, and, using one (1) cube on each side of the rubber band, cool the length of the rubber band by rubbing one (1) cube on each side simultaneously. Cool the rubber band for at least one to two minutes, and observe/record the length of the jug again.
6. Allow the rubber band to return to room temperature.
7. You will now heat the rubber band using the blow dryer. Turn the blow dryer on. Using a gradual but consistent motion, move the blow dryer up and down the length of the rubber band in order to heat it. Continue heating the rubber band for a period of between 10-30 seconds. Observe/record the length of the jug again.
8. Repeat the cooling and heating process outlined in Steps 5-7 at least three more times, until your results for the distance change are consistent. You may need to change the initial reference point, since the rubber band tends to stretch more over time.
Discussion
1. Does your data support your hypothesis?
Yes my data does support my hypothesis
2. Explain what seems to have happened; what did the rubber band do?
In this experiment we can see what happens to the length of a rubber band if we heated or cool it. When I put heat into the rubber band, when i put an ice the rubber band is contracted.
3. Explain at a molecular level what most substances do when heated and cooled.
Molecular expand when they are heated and contract when they are cooled.
4. Relate what happened in terms of entropy. (Hint: Look at the introduction again. Be sure to include something about temperature and entropy.)
When the temperature the entropy low the temperature is decreases is going to be high entropy.
5. What would you expect to happen to the temperature of a rubber band if you suddenly stretched it? (Try it!)
When the rubber band stretched produce heat the temperature increased.
6. How about if you slowly stretched a rubber band and then suddenly let it contract?
7. Shrink- wrap uses heat (without melting it) to seal something in a special type of plastic. Explain how this must work.
8. What are the usual units of entropy?
9. Write a mathematical formula that includes entropy. Explain each of the terms in the formula.
Lab 10
Entropy
Introduction: Connecting Your Learning
People sometimes mistakenly think that entropy, “S,” means disorder or messiness. There is some truth to this perception. For example, a pile of bricks and mortar will never spontaneously self-assemble into a building; whereas, even if left alone, a building will eventually be reduced to a pile of rubble. In other words, entropy proceeds inexorably toward the maximum without outside input. “S” can be more accurately described as the number of possibilities for a given system. Thus, the higher the temperature, and the more the particles will usually move (which means that they have more possibilities for where they might be at any given moment), the higher the S. The opposite is true for colder temperatures. Some salts will dissolve spontaneously even though they require heat to dissolve simply due to the large increase in entropy, as the individual ions are no longer limited to the rigid crystal lattice ionic structure and now have many more possibilities for where they may be within an aqueous solution. This is how those one-use disposable cold packs work. They typically have an ionic solid such as ammonium chloride within a pouch in which there is also a smaller pouch of water. By squeezing the pouch, you break the water-filled pouch inside, dissolving the ammonium chloride. Since this is an endothermic reaction, heat is absorbed from the surroundings, making the pouch cold.
An interesting phenomenon about wool is that it will curl or uncurl because of entropy changes, as seen below:
Do you see why wool shrinks when washed in hot water?
In this lab, you will investigate how entropy relates to the following experiment using a rubber band.
Resources and Assignments
Multimedia Resources None
Required Assignments Lab 10 Report
Materials (Lab Kit) • Rubber band
• Ruler
Materials (Student supplied) • One gallon milk or water jug
• Tap water
• Door handle
• Ice
• Blow dryer
Focusing Your Learning
Lab Objectives
By the end of this lesson, you should be able to:
1. Investigate an aspect of entropy.
2. Apply an understanding of entropy to a system.
Procedures
1. Cut the rubber band so that you have a rubber strip instead of a rubber band.
2. Fill the jug half-full of tap water.
3. Tie one end of the rubber band to the jug, and the other end to a sturdy door handle or other device you can use to “hang” the jug from.
4. Make an initial measurement as a reference point for the position of the jug in terms of its distance from the door handle. In other words, you want to know how long the rubber band allows the half-full jug of water to hang from the door handle.
Predict what will happen if the rubber band is heated (will it get longer or shorter?) and if the rubber band is cooled. Now you will perform this experiment:
5. Take two (2) ice cubes, and, using one (1) cube on each side of the rubber band, cool the length of the rubber band by rubbing one (1) cube on each side simultaneously. Cool the rubber band for at least one to two minutes, and observe/record the length of the jug again.
6. Allow the rubber band to return to room temperature.
7. You will now heat the rubber band using the blow dryer. Turn the blow dryer on. Using a gradual but consistent motion, move the blow dryer up and down the length of the rubber band in order to heat it. Continue heating the rubber band for a period of between 10-30 seconds. Observe/record the length of the jug again.
8. Repeat the cooling and heating process outlined in Steps 5-7 at least three more times, until your results for the distance change are consistent. You may need to change the initial reference point, since the rubber band tends to stretch more over time.
Assessing Your Learning
Discussion
1. Does your data support your hypothesis?
2. Explain what seems to have happened; what did the rubber band do?
3. Explain at a molecular level what most substances do when heated and cooled.
4. Relate what happened in terms of entropy. (Hint: Look at the introduction again. Be sure to include something about temperature and entropy.)
5. What would you expect to happen to the temperature of a rubber band if you suddenly stretched it? (Try it!)
6. How about if you slowly stretched a rubber band and then suddenly let it contract?
7. Shrink- wrap uses heat (without melting it) to seal something in a special type of plastic. Explain how this must work.
8. What are the usual units of entropy?
9. Write a mathematical formula that includes entropy. Explain each of the terms in the formula.
Lab Report
Make sure to complete a full lab report and submit it via email by the due date.
Submission
Important information: Please follow the procedure below in the completion of your assignments.
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