Pressure and Phase Experiment Questions Consider the experiment where a test tube filled with water is inverted in a beaker of water . (The following figures are not to scale of actual apparatus.)
At time t=0, the instantaneous snapshot is shown here:

After allowing sufficient time to elapse, equilibrium is reached and is shown here:

Questions:


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*Is the upper part of the test tube (indicated by the red arrow) filled with water vapor, or is it vaccuum? Is the pressure there equal to the vapor pressure?

*Is the water boiling at the upper part of the test tube (indicated by the red arrow)? If so, why does it not look as "vigorous" and "bubbly" as water boils in the kitchen at (100 degree C and 1 atm)?
Helpful references, including book chapters, that may help in understanding this are also greatly appreciated.
 A: In many discussions the difference doesn't matter, so we might call it a vacuum.  But you're correct that it will contain water vapor.  Yes, the pressure is equal to the vapor pressure.  
When water is boiling on the stove, there is no equilibrium.  The stovetop is hot and the atmosphere is cool.  The temperature gradient is driving the boiling process.  You say this tube is in equilibrium, so nothing is "boiling" any longer. 
Another difference is that on the stovetop, the boiling process is happening at the bottom of the pan (where the energy is entering).  The bubbles move through the water to the surface and churn the entire vessel.  In your tube, the pressure on any sub-surface water is above the vapor pressure.  Only at the very top is the pressure low enough to drive the transition.  Unless the void space is large, any boiling would be over with quickly.  You might not see any activity.
See also:
Why doesn't water in water barometer boil?
http://www.physlink.com/Education/AskExperts/ae443.cfm
