Kitchen Science?

This really happened! Sunday, while preparing for our family lunch, my mother noticed that the electric skillet she had cooked the roast in was cooling. She asked me to take the lid off. I pulled, and tugged, and used a screw driver. It would not come off.

This really happened! Sunday, while preparing for our family lunch, my mother noticed that the electric skillet she had cooked the roast in was cooling. She asked me to take the lid off. I pulled, and tugged, and used a screwdriver. It would not come off.

Well, we tried cooling it with water in the sink. And that did not work. Then, my wife, a librarian, Googled: Pot lid stuck. The web page it pointed to was something about Kitchen Tips. They said to reheat the pot and when it came to a boil the lid came right off.

There is some real good science here. I have not taught chemistry in many years, but after my wife told me about the tip from the web page, it hit me. It is a perfect example of the Gas Law. Take a look at this Java applet to visualize the science the experienced first hand in the kitchen today. Move the temperature slider to the right and notice the increase in pressure. This is what happened to the pot my family was using to cook the meat in. As the meat cooked in the pot, the temperature increased. This volume of the pot remained constant. However, when the temperature of the pot was reduced, the pot's lid was not removed and (volume remains constant) the pressure inside the pot dropped. This is caused when the number of collision between the molecules in the pot were reduced. Let collisions of molecules produced let pressure. This caused a vacuum to be formed inside the pot sealing it. We could not break the seal with screwdrivers, knife blades or anything we tried. I wish I had my digital camera to take a picture of what it looked like. Turning the heat back on the pot called the molecules of gas to increase their kinetic energy. This increase in temperature increased the pressure inside the closed cook pot. We noticed that steam was coming out of the pot after about 4 minutes of heating. The lid was easily removed.

Conclusion: If the Volume of a gas remains constant, and temperature is increased the pressure increases proportionally to the increase in temperature.