`Relationships:  Pressure, Volume, and TemperatureSamuel E. Hall, Jr.                       Chicago H. S. for Ag Sciences                                          11325 W. 111th Street                                          Chicago, Illinois 60655                                          312-881-5000Objectives:Grade Level:  Sophomore chemistryStudents will be able to state the relationships of pressure to volume and pressure to temperature, and volume to temperature for a gas. Materials needed:Per team:  1 small round balloon           24 inch length of string           1 meter stick           1 fire syringe Charles Law demo apparatus (available from Cenco)           4-5 inches of sewing threadStrategy:     The activities are such that the students will discover the relationships stated in the objectives above.  First, Ask the students to inflate a rubber balloon to its fullest diameter.  The students should measure the circumference of the round part of the balloon.  Although you purchase round balloons, the balloons will probably be pear shaped.  We are interested in the round part.  Place the balloon into the freezer or ice chest partially filled with ice.  We need to bring the temperature of the gas in the balloon down as far as possible, let them stand and go to the next activity; tell the students that we will come back to this one.  Don't answer any questions that they ask about the first activity - for now they should follow directions.      The second activity should begin with a demonstration of the use of the fire syringe.  This apparatus is made of a rod with a "T" shaped handle at one end and rubber gaskets at the other end.  Another part of the apparatus is made of a thick walled glass tube shaped like a test tube.  The third part is a metal tube fitted with a rubber foot so that the tube assembly does not slip from the table in use.  Just above the rubber foot is a viewing window so that you can observe what is happening in the glass tube.  The other end is open to receive the glass "test tube" like part.  Show the students that the thread will burn; use a match or "bic" lighter.  Then insert a fresh length of thread into the glass tube - insert the rod - place this assembly into the metal tube.  Hold the metal tube vertically on a flat surface with one hand and with the other hand hold the plunger.  Push down with a reasonable amount of force.  Ask the students to observe the view window on the metal tube.  Do not mention the fact that the gas in the tube is compressed.  Give one fire syringe to each group and ask them to record the groups' observations.      Let's go get those balloons.  Measurements of circumference should be made as soon as possible after they come out of the cooler.  Record observations.  Make comparisons of circumference before and after cooling. Conclusions:Relative to the balloons, I want students to realize that as the temperature decreased - the volume of the balloon also decreased.  Use "V" and "T" to mean volume and temperature respectfully.  V/T (read volume divided by temperature) of the initial situation is equal to V/T of the second situation (after cooling).  Discuss relationships;  V/T = c ("c" is constant); V/T = V'/T'. Relative to the fire syringe, I want students to realize that as the pressure increased the temperature also increased.  P/T = c and P/T = P'/T'.All of the above should take approximately 40 minutes.  On the next day have the students perform a pressure - volume activity. `