Stephen A. Lawrence <sa...@pobox.com> wrote:
> Jed, it's a container, with all the walls at several hundred degrees C or > higher; the bottom's in contact with the burner and is probably at about > 1000 C. > > There is nothing inside the container except gas: Gaseous water. > > Yet you are claiming the gas inside the container can't be hotter than 100 > C! > If it gets any hotter, the vapor expands and more of it leaves the container. Water vapor at 1 atm cannot be hotter than 100 deg C. The inside of the pot is much hotter of course, since there is heat radiating from the bottom. I meant that if you isolate the steam and take its temperature, it will be 100 deg C. It is, of course, impossible to do that inside the kettle itself. You can only measure some average temperature of the metal and vapor. You have to spray some water in, have it exit the by a hose, and measure the temperature some distance from the hot metal. The kettle temperature might be 500 deg C, but the steam will never be more than 100 deg C, unless you confine it and raise the pressure. > That's magic -- it violates the laws of thermodynamics bigtime. > > How can water vapor be so magical? No other gas behaves that way -- no > other material behaves that way! > All gas behaves that way. There is no violation of thermodynamics, because the vapor occupies more and more space, until eventually it is close to a vacuum inside the kettle. Confine it so that it cannot occupy more space and then the temperature rises. Reduce the pressure around the water to the vacuum of interplanetary space and the liquid boils at any temperature. - Jed
