A. Procedure (You will work in groups of three or four)

TAKE THE AIRPLANE PROVIDED, WIND UP THE PROPELLER AND LET IT FLY!!
DID YOU DO WORK WHILE TURNING THE PROPELLER AND STRETCHING THE RUBBER BAND?
WHEN IT LANDS, IMMEDIATELY FEEL THE RUBBER BAND!!
DID THE RUBBER BAND HEAT OR COOL WHILE THE PLANE WAS FLYING AND THE RUBBER BAND CONTRACTING?

   1. Each person take a rubber band and stretch it.  Holding it
      stretched, immediately touch your upper lip.  

   2. Let the rubber ban contract to its original size and again
      immediately touch it to your upper lip.  

   3. Repeat Steps 2 and 3 for a total of three times, 
      recording results on the Table below:
    ________________________________________________________________
   |	      |			         |                          |
   |  Trial   |       Stretching         |         Contracting      | 
   |__________|__________________________|__________________________|
   |          |                          |                          |
   |    1     |                          |                          |
   |__________|__________________________|__________________________|
   |	      |                          |                          |
   |    2     |                          |                          |
   |__________|__________________________|__________________________|
   |          |                          |                          |
   |    3     |                          |                          |
   |__________|__________________________|__________________________|

   4. Discuss with your group these points:

      a. When stretching, what is the sign of  H and  G?  Record
         on your Data Sheets.

      b. When released and contracting, what is the sign of  H
         and  G?  Record on your Data Sheets.

      c. Now using the Gibbs equation from class predict what
         the sign of  S must be for each process:  stretching
         and contracting.  Record on Data Sheets.

      d. Try to correlate your results in part 4. c. above with
         the molecular structure of the rubber band.  HINT: 
         Rubber is a polymer.  Molecules in polymers can
         stretch, contract, and twist.  Draw a picture of the
         molecules of the rubber band in the stretched form and
         the contracted form on your Data Sheets.




Chemistry 102	    LAB REPORT 2		   Name_______________
Date ____________       (25 points)          Section_______________


           THERMODYNAMICS OF RUBBER BANDS


1. (8 points) Complete the following table with the 
	      correct sign for the energy change:


	    |---------------------------------------------|			
            |	           RUBBER BAND                    |
            |-------------------|-------------------------|
            |	STRETCHING 	|	CONTRACTING       |
------------|-------------------|-------------------------|
delta "H"   |                   |                         |
------------|-------------------|-------------------------|
delta "G"   |                   |                         |
------------|-------------------|-------------------------|
  

2. (4 points) What is the sign for delta "S" for:


   Stretching: ________   Contracting:  ________


3. (4 points) What is your conclusion on the molecular 
              entropy change for the rubber band?


   When stretching? __________________________________



   When contracting? _________________________________


4. (4 points) Draw a picture of the molecules of the rubber 
	      band in the stretched form and the contracted 
	      form:

         









5. (5 points) "DESCRIBE AN EXPERIMENT" of your choosing
 which does not use a rubber band or rubber and 
exemplifies the principals we have seen in this experiment,
 i.e., entropy, enthalpy and free energy?