Gas pressure rises with temperature
A quick, dramatic demonstration to show the pressure of a fixed volume of gas increases with temperature.
Apparatus and materials
Tin with lid
Health & Safety and Technical notes
Safety screens are needed with the class sitting well back.
Heat-proof gloves should be available for retrieving the lid and the hot tin.
The tin should have a well-fitting, push-in lid.
To ensure a reliable result, it is not unknown for teachers to secrete a small amount of water in the tin before sealing with the lid. It is helpful to try out this demonstration before the lesson, allowing enough time for the tin to cool down again! (It has not been unknown for the lid to stay fixed in place even after several minutes heating of dry air only.)
a Show the tin to contain (or appear to contain) only air before gently pushing in the lid.
b Place on the tripod and then heat using the Bunsen burner until the lid is blown off.
Apart from being dramatic - and thus memorable - this demonstration provides an opportunity to get students thinking about what has happened in terms of molecules.
Help students to understand that as the molecules gain kinetic energy so they move ever faster, hitting the walls of the tin, and its lid, both harder and more often. This means the pressure rises. Pressure rises until it is sufficient to force the lid off.
This experiment was safety-checked in March 2006