In a lab, a 1L balloon was placed over an Erlenmeyer flask at 100 degrees celsius.

Question

As the temperature of the flask was cooled the balloon was pulled into the flask as the volume of the air in the flask reduced.

What are the changing and constant variables? Why did the volume of the air in the flask reduce?

Answer 1

The only constant is the total amount of gas in the balloon and flask.  The other variables are pressure, volume, and temperature, which are all changing.

 

The gas obeys the law

 

PV/T = nR = constant

 

n = number of moles

R = universal gas constant

 

As the gas temperatures drops, the pressure also drops, since the kinetic energies of the gas molecules are lower at lower temperature, resulting in lower momentum of gas molecules bombarding the skin of the balloon.  As the pressure applied against the skin of the balloon drops, the balloon shrinks elastically as it "unstretches", resulting in lower volume.