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I mean what will be the situation inside? All water vaporized, Equilibrium, Temperature-pressure situation.. boiling point increase/decrease?

Thanks for your time.

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this might answer your questions wiki.answers.com/Q/How_does_a_pressure_cooker_work –  anna v Mar 28 '12 at 17:01
Thanks for the link –  eagleye Mar 29 '12 at 7:29

1 Answer 1

up vote 5 down vote accepted

You need to look at the PT phase diagram for water e.g. http://www.standnes.no/chemix/english/phase-diagram-water.htm

At temperatures below the critical point the water will boil until the pressure rises enough to bring the water and vapour into equilibrium, so you'll have a mixture of water and steam. Above the critical point water and steam merge into a single phase i.e. there is no distinction between the liquid and vapour.

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What do you mean by "the pressure rises enough to bring the water and vapour into equilibrium"? There will be an initial heatup period when the water is subcooled, at which dP/dQ will be smaller than after the boiling starts. Maybe that's what you meant - that it heats up until it becomes a saturated mix. But the vapor does not exist before that point (as I assume the other half is air). The vapor is always saturated. Because of that, your statement is difficult to interpret. –  Alan Rominger Mar 28 '12 at 17:57
@AlanSE I think that John meant exactly that –  eagleye Mar 29 '12 at 7:30
it was slightly clumsy wording, but I think the meaning is clear. Even below 100C the liquid water will be in equilibrium with water vapour in the air above it. All that happens as you raise the temperature is that the partial pressure of the water vapour rises. If you raised the temperature very slowly you'd never see the water boil, in the sense of bubbling, because evaporation would be fast enough to keep the water and vapour in equilibrium. –  John Rennie Mar 29 '12 at 8:21

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