Eli5 what would happen if you had water in a completely sealed container and brought it past boiling temp

Question

Would it just turn into a pressurized container full of steam? Would the water stay water but just like, really hot?

In: 98

Answer 1

The science is kind of important here, and its being omitted by many of the top comments.

We state that water boils at 212 degrees F or 100 degrees C but what we don’t generally reference is that those numbers are assuming we are at atmospheric pressure at sea level. We know that water boils at a lower temperature at higher altitudes, you can see this in some recipes or cooking instructions where there is a separate set of instructions for high altitude cooking specifically because when you cook something in boiling water at higher elevation(lower pressure) it doesn’t reach 212 degrees, more like 190 degrees or even lower.

By the same rules, if you increase the pressure you increase the temperature that water boils. This means that as the pressure cooker heats up you cause some water (liquid) to boil and turn into water vapor(steam). Under normal circumstances water turning to steam increase in volume tremendously, around 1800 times as much volume.

So in your pressure cooker you create this moving target of what is the boiling point, as the pressure cooker attempts to increase the amount of water vapor(boiling water), the pressure goes up which means the temperature of the water continues to increase beyond 212 without boiling. Without a way to exhaust water vapor(like the relief valve) or turn off the heat(temperature controls in the electronics of the unit), the temperature and pressure would continue to rise until the device failed.

In reality, you couldn’t realistically reach a temperature where most of the water turned into water vapor, the pressure and temperature would be astronomical to support the vapor not condensing back into liquid water. Your at home pressure cooker still has overwhelmingly water in it until you open the vent on the cooker which lets water vapor out. At that point the water inside will instantly start to boil(its hotter than 212 degrees as discussed and the pressure was just reduced back to atmospheric) and much of the remaining water will quickly boil off.