Volume change during boiling

  When you prepare food with a steam or pressure cooker, the cooking time is shorter than in a conventional cooking pot. This is because the gaseous water resulting from boiling of water cannot escape from the pot. So, higher temperatures than usual can be achieved. In the following experiment, you will investigate what happens when you replace the pressure cooker by a stoppered ampoule and by a closed air balloon.


1.     Put a few drops of water into the ampoule and close it with the stopper.                                   2.     Heat the water in the ampoule above the tea light. Make sure that the opening of the ampoule is not directed at other people.                                                  (more see below)


3.  Put some water in a balloon and knot it. Keep the second balloon empty and also knot it.

4.      Heat the two closed balloons in a microwave oven.

5.     Open the microwave oven and wait until no more changes occur.


1.     Write down your observations and explain them.

2.     How do the smallest particles differ in the liquid and in the gaseous state?

3.     What happens at particle level during the transition from the liquid to the gaseous state?

First published: 2004                                                               Last modification: 11.06.2014