Equipment:

1. Gallon can with screw top
2. Bunsen burner(with sparker) and ring stand or electric hot plate (if no gas line)
3. Hot mitt
4. Water
5. Ice water bath (optional but recommended)

Demo:

Boil a small amount of water in the open can. When water vapor displaces most of the air, indicated by the presence of steam, remove the can from the heat and cap it. After placing in an ice bath or leaving to sit, the can will collapse in a couple of minutes.

Explanation:

When the can is taken off the heat and capped the water vapor will condense back into water as it cools. The can is malleable enough to be crushed by the pressure difference between the inside of the can (low pressure) and the outside of the can (high pressure). We can use the ideal gas law to describe this interaction,

where P is the pressure inside the can, V is the volume of the can, and T is the temperature of the gas. We can see that a decrease in temperature will result in a decrease in pressure. By placing the can in an ice bath, this effect is accelerated and results in a more dramatic demonstration.

Notes:

• Allow plenty of time for the can to heat up, especially if using a hot plate.
• Use caution when caping the can .

Written by Lydia Seymour