prabhat rao
11th May 2008 - 08:21 AM
a pressure cooker, which is filled with 1/4 of water and remaining 3/4 is filled with air. Then it is closed that no water vapor or air can escape. The cooker with water is slowly heated. At what temperature will water start to boil?
Enthalpy
11th May 2008 - 05:05 PM
Usual water will first release dissolved gases, probably a bigger volume than the air originally in the cooker. OK, it was pure water.
The amount of air just tells to neglect the expansion of liquid water.
Stepwise:
at +100°C, the air pressure is 373/298=1.25bar (if you live in Calcutta, replace 298K by 313K in the shade) (but on Mount Everest, you don't need 100°C).
To boil at 1.25bar, water needs a temperature of 105.8°C, from the approximate formula (°C/100)^4.
You may unroll one loop again with 273+106 instead of 373K.
This supposes that the air has the same temperature as the water: not obvious.