Gas Laws on a Microwaved Container

This common occurence is a a good illustration of gas laws.  A container is heated, e.g. in a microwave, while it is open to the atmosphere.  When the container contains hot gas in pressure balance with the outside atmosphere, the container is closed.  As the gas in the container cools, its internal pressure decreases according to Gay-Lussac's law, which states that the pressure exerted on a container's sides by an ideal gas is proportional to the absolute temperature.  The net result is often that the container (like the butter tub in the picture) is deformed by the pressure of the outside atmosphere.